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

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

[0001] The present invention relates to a method for producing a lithium-lanthanum-zirconium composite oxide powder and to a lithium-lanthanum-zirconium composite oxide powder.

[0002] Li ７ La ３ Zr ２ O １２ Lithium-lanthanum-zirconium composite oxide powder (hereinafter referred to as "LLZ powder") having the basic composition shown above 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 material (so-called co-material) added to conductive pastes used to form internal electrodes of such capacitors (see, for example, Patent Documents 1 to 3).

[0003] Conventionally, the method for producing such a material involves mixing a zirconium compound, a lanthanum compound and a lithium compound, and then firing the mixture for a long period of time.

[0004] For example, in Patent Document 1, lithium carbonate, lanthanum hydroxide, and zirconium oxide are prepared as raw materials for a solid electrolyte, and these raw materials are mixed to form a Li ion conductive compound having a composition of Li ７ La ３ Zr ２ O １２ The method disclosed therein includes weighing out a predetermined amount of the compound so as to obtain a mixture, and then heating the mixture to 900°C in an air atmosphere, maintaining the mixture for 5 hours, and then allowing it to cool naturally to obtain a Li ion conductive compound.

[0005] Furthermore, for example, Patent Documents 2 and 3 disclose the following method. First, a mixed material is prepared by weighing and mixing lithium carbonate, lanthanum hydroxide, and zirconium oxide in predetermined amounts so as to achieve the stoichiometric composition of LLZ. This mixed material is then mixed with a predetermined amount of ethyl alcohol using a nylon pot and zirconia beads 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 a calcined LLZ powder. Next, this calcined LLZ powder is mixed with a methyl ethyl ketone / toluene mixed solvent using a nylon pot and zirconia beads, pulverized, and dried to prepare an LLZ powder.

[0006] Furthermore, 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, and the mixture is heated at 600°C / hour and held at 900°C for 6 hours. After that, approximately half of the weight of the resulting 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 the mixture is pulverized in a grinding mill for 30 minutes, and then placed again in the alumina crucible, and the temperature is raised at 600°C / hour and held at 1125°C for 6 hours to obtain a powder. Thereafter, approximately half of the weight of the 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 sieving this powder, Al ２ O ３ The resulting mixed powder is press-molded using a mold to form pellets, and the pellets are embedded in the mixed powder, heated at a rate of 60°C / hour, and maintained at 1180°C for 36 hours to obtain a lithium-lanthanum-zirconium composite oxide.

[0007] Furthermore, Patent Document 5 discloses a method in which a mixture obtained by mixing lanthanum zirconate, lithium carbonate, and lanthanum hydroxide is mixed in a wet ball mill for 24 hours, and then dried at 100°C for 5 hours to prepare a raw material mixed powder, and the obtained raw material mixed powder is placed in a crucible, heated in an electric furnace at 750°C for 12 hours, and then naturally cooled.

[0008] Furthermore, Patent Document 6 discloses a method in which lanthanum-containing zirconia powder having an average particle size of 100 nm is produced by a coprecipitation method, mixed with alumina powder and lithium carbonate powder, and fired at 700° C. for 12 hours.

[0009] Patent Documents 5 and 6 describe that it is difficult to obtain the target LLZ product when fired for a long period of time at a high temperature exceeding 1000° C. because lithium components are dispersed. 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 dispersion of lithium components at a firing temperature of less than 1000° C.

[0010] JP 2015-130481 A JP 2017-147398 A JP 2018-041902 A JP 2011-051800 A JP 2014-172812 A JP 2018-065704 A

[0011] 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, particularly about 30 nm to 300 nm, for various applications. However, in the manufacturing methods disclosed in Patent Documents 1 to 6, a mixture of LLZ raw materials is heated at high temperatures for a long period of time while being left stationary, and therefore the LLZ inevitably becomes large lumps after heating.

[0012] Therefore, in order to obtain the small particle size LLZ powders currently 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 using the aforementioned method to produce LLZ powder with a D50 of 0.2 μm to 12.1 μm, which is then used in the solid electrolyte layer and internal electrode of a solid ion capacitor. In this specification, the term "pulverization" refers to the process of crushing a substance by applying an external force to reduce its size to a size smaller than its original size. Furthermore, the term "disintegration" refers to the process 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.

[0013] Generally, when a ceramic powder is subjected to a pulverization process to obtain a 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 then pulverize it for a long time with an extremely strong force using a media mill or the like, and as a result, a large number of microcracks and highly active surfaces are generated on the surface of the obtained ceramic powder, and the problem of lithium components eluting into the solvent is widely known. Generally, the smaller the particle size of the ceramic powder, the higher the surface activity. However, in the case of LLZ powder in particular, the lithium components on the surface of the powder are easily dissolve in CO ２ and H ２ It reacts with O to cause deterioration of the ceramic, and also causes lithium to escape, resulting in defects in the crystal structure, which in any case has a negative effect on storage stability.

[0014] Therefore, when used as a co-material in a conductive paste for the internal electrodes of a capacitor, for example, the lithium component eluted from the surface of the LLZ powder reacts with the organic vehicle in the conductive paste, causing a serious problem of gelling of the conductive paste.

[0015] Furthermore, in industrial production of small particle size LLZ powder, which has seen an increase in demand recently, it is preferable that the production time be as short as possible.

[0016] In view of these problems, the present invention aims to provide a method for efficiently producing a small-particle size lithium-lanthanum-zirconium composite oxide powder that exhibits excellent storage stability while suppressing lithium scattering. Another object of the present invention is to provide a lithium-lanthanum-zirconium composite oxide powder that exhibits excellent storage stability by minimizing powder surface activity despite its small particle size.

[0017] 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. －３０ The present inventors have found that by using a method for producing a lithium-lanthanum-zirconium composite oxide powder, 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, and have completed the present invention. The method 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 dispersed in the carrier gas at a temperature of 900°C or more and 1200°C or less for a time of 1 second to 30 seconds 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.

[0018] That is, the present invention (1) comprises 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. －３０a 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 and heating the precursor powder dispersed in the carrier gas 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 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.

[0019] The present invention (2) also provides the method for producing the lithium-lanthanum-zirconium composite oxide powder of the present invention (1), wherein 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.

[0020] The present invention (3) also provides the method for producing the lithium-lanthanum-zirconium composite oxide powder of the present invention (1), wherein 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.

[0021] 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), 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.

[0022] 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), 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 or more and 300 nm or less.

[0023] 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), wherein the lanthanum zirconate powder is obtained by heating a coprecipitate of a lanthanum compound and a zirconium compound.

[0024] 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 ratio measured by the following method of 1. <Method for Measuring Viscosity Change Ratio> 100 parts by mass of nickel powder having an average particle size of 0.3 μm, 5 parts by mass of acrylic resin (a methacrylic resin having a weight-average molecular weight of 40,000 or more and 50,000 or less 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, and the viscosity immediately after preparation and the viscosity after storage at 25° C. for 1 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 after 1 week to the viscosity immediately after preparation is calculated as the viscosity change ratio.

[0025] According to the production method of the present invention, it is possible to efficiently obtain a small-particle size lithium-lanthanum-zirconium composite oxide powder that exhibits excellent storage stability while suppressing lithium scattering. Furthermore, despite its small particle size, the lithium-lanthanum-zirconium composite oxide powder of the present invention exhibits minimized powder surface activity and exhibits excellent storage stability.

[0026] The present invention will be described in detail below, but the present invention is not limited thereto.

[0027] The LLZ powder according to the present invention is ７ La ３ Zr ２ O １２The powder has a basic composition of 30 nm or more and 1.0 μm or less, particularly 30 nm or more and 300 nm or less, and is characterized by excellent storage stability. In this specification (the present invention), the powder is observed using a scanning electron microscope (for example, SU-1510 manufactured by Hitachi High-Technologies Corporation), and 100 particles constituting the powder are randomly selected from the observation to measure their particle diameters. The average particle diameter is calculated as the cumulative 50% particle diameter on a number basis based on the particle diameters. The particle diameter 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 LLZ powder but also for the average particle diameter of the nickel powder described below.

[0028] 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 art, a ratio that approximates this ratio may also be used. Furthermore, a portion of each element in the basic composition may be substituted with another element. Examples of such other elements include aluminum. Furthermore, when the LLZ powder of the present invention is used for a solid electrolyte, it is preferably a cubic crystal, but this is not necessarily limited to this. If a tetragonal LLZ powder is desired, the tetragonal crystal may be obtained by appropriately adjusting the heat treatment conditions, etc.

[0029] <Production Method of the Present Invention> The production method of the present invention includes 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, respectively; 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. －３０ The method for producing a lithium-lanthanum-zirconium composite oxide powder includes: 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, and heating the precursor powder dispersed in the carrier gas 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 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.

[0030] As described above, the manufacturing method of the present invention is characterized by using a small-particle lanthanum zirconate powder, coating its surface with a lanthanum compound and a lithium compound in advance, and then heating the powder in a gas phase under a controlled atmosphere. Therefore, due to the high surface activity of the lanthanum zirconate powder, the lanthanum compound and lithium compound easily diffuse into the lanthanum zirconate powder. Furthermore, due to the short distance from the surface to the center (innermost part) of each particle constituting the powder, the lanthanum compound and lithium compound easily reach the center (innermost part) of each particle constituting the lanthanum zirconate powder. Therefore, even when the precursor powder is heated at a temperature of 900°C to 1200°C for a short time of 1 second to 30 seconds, the lanthanum compound and lithium compound easily diffuse throughout the entire interior of each particle constituting the lanthanum zirconate powder, reducing the amount of lithium compound scattered, and enabling efficient production of the desired LLZ powder.

[0031] Each step constituting the manufacturing method of the present invention will be described below.

[0032] The manufacturing method of the present invention may include the first, second, third, and fourth steps described below, but may also include an additional step before the first step, an additional step between the above steps, or an additional step after the fourth step.

[0033] [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.

[0034] (Lanthanum zirconate powder) The average particle size of the lanthanum zirconate powder prepared in step 1 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 step 3 described below, making it easier to obtain LLZ even with a short heating time.

[0035] Lanthanum zirconate powder may be manufactured, or commercially available lanthanum zirconate powder may be used. If the average particle size of commercially available lanthanum zirconate powder is greater than 200 nm, it may be pulverized and / or crushed by a suitable known method such as a ball mill or a bead mill so that the average particle size falls within the above-mentioned range.

[0036] 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 under a scanning electron microscope.

[0037] Lanthanum zirconate powder can be produced by any method, including heating a mixture of a zirconium compound and a lanthanum compound. However, it is particularly preferred to use a coprecipitation method, as described in Patent Document 6, which is a widely known powder production method, to heat a coprecipitate of a lanthanum compound and a zirconium compound. When preparing lanthanum zirconate powder using this method, it is preferable to prepare a coprecipitate having an average particle size of 20 nm to 200 nm. If the average particle size of the coprecipitate is greater than 200 nm, it is adjusted to 20 nm to 200 nm by pulverization and / or crushing. By controlling the average particle size of the coprecipitate within the above range, heating facilitates the production of lanthanum zirconate powder having an average particle size of 20 nm to 200 nm. Even if the average particle size of the resulting lanthanum zirconate powder is greater than 200 nm, the average particle size can be easily adjusted to 20 nm to 200 nm by pulverization and / or crushing.

[0038] The zirconium compound used in producing lanthanum zirconate is not particularly limited, and examples thereof include zirconium oxide, zirconium hydroxide, zirconium sulfate, zirconium carbonate, zirconium chloride, and zirconium nitrate. The zirconium compound may be in 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 greater than 100 nm, it can be used after being adjusted to within the above range by pulverization and / or crushing. 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.

[0039] The lanthanum compound used in producing lanthanum zirconate is not particularly limited, and examples thereof include lanthanum oxide, lanthanum hydroxide, lanthanum sulfate, lanthanum carbonate, lanthanum chloride, and lanthanum nitrate. 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. Furthermore, when using a lanthanum compound in a coprecipitation method, the lanthanum compound preferably has high dispersibility in the liquid, and is preferably in a sol state.

[0040] (Lanthanum Compound) The lanthanum compound prepared in the first step is not particularly limited, and for example, the above-mentioned lanthanum compounds can be used.

[0041] (Lithium Compound) The lithium compound prepared in the first step is not particularly limited, and for example, lithium carbonate, lithium hydroxide, lithium nitrate, lithium sulfate, or lithium chloride can be used. The lithium compound may be in 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 greater than 100 nm, it can be used after being adjusted to within the above range by pulverization and / or crushing.

[0042] [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.

[0043] The deposition method is not particularly limited. For example, when the lanthanum compound and / or lithium compound prepared in the first step is in the form of powder, the powder can be mixed with lanthanum zirconate powder using a ball mill, a bead mill, or the like, to mechanochemically deposit the lanthanum compound powder and / or lithium compound powder on the surface of the lanthanum zirconate powder, thereby producing a precursor powder.

[0044] Alternatively, a solvent may be prepared that dissolves a lanthanum compound and / or a lithium compound but not a lanthanum zirconate powder, and the lanthanum zirconate powder may be introduced into the solution in which the lanthanum compound and / or the lithium compound has been dissolved. After that, the lanthanum compound and / or the lithium compound may be precipitated on the surface of the lanthanum zirconate powder by a method such as reduction or drying the solution (solvent), thereby producing a precursor powder.

[0045] Alternatively, 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 a lithium compound may be kneaded into the organic binder and then coated on lanthanum zirconate powder, thereby generating a precursor powder in which the lanthanum compound and / or lithium compound is adhered to the surface of the lanthanum zirconate powder via the organic binder.

[0046] The above methods can also be used in combination. 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.

[0047] The second step described above is preferably a step of depositing a lanthanum compound and a lithium compound on the surface of lanthanum zirconate powder, and then calcining the lanthanum zirconate powder coated with the lanthanum compound and lithium compound 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 any suitable atmosphere, such as air or nitrogen.

[0048] By carrying out the above-mentioned calcination, the lithium compound and the lanthanum compound can be more firmly adhered 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 compound and the lanthanum compound are less likely to dissociate from the surface of the lanthanum zirconate powder, making it easier to obtain an LLZ powder. Furthermore, because the lithium compound and the lanthanum compound 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 a carrier gas, making it easier to improve the dispersibility of the precursor powder in the carrier gas, and the particles constituting the obtained LLZ powder are less likely to bond or aggregate with each other.

[0049] Furthermore, the water content and hygroscopicity of the precursor powder can be reduced by calcination, which improves dispersibility when the precursor powder is dispersed in a carrier gas in the below-described Step 3. Therefore, it becomes easier to eliminate the need for pulverization and / or crushing treatment after Step 3, which can suppress the activity of the powder surface of the LLZ powder, and it becomes easier to improve storage stability.

[0050] Furthermore, by carrying out the above-described calcination, the lithium compound and lanthanum compound deposited on 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 deposited on the surface of the powder is enhanced, making it easier to obtain the desired LLZ powder even if the heating time is short.

[0051] 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, subsequently 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 or more and 300 nm or less.

[0052] Even if calcination is not performed, secondary particles may be generated by the above-mentioned coating process, etc., and therefore, the average particle size of the precursor powder can be adjusted to a specific range by pulverization and / or crushing, as necessary. That is, the above-mentioned second step can be a step of coating the surface of lanthanum zirconate powder with a lanthanum compound and a lithium compound, followed by pulverization and / or crushing to produce a precursor powder having an average particle size of 30 nm to 300 nm.

[0053] The average particle size of the precursor powder produced in the second step 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.

[0054] [Third Step] In the third step of the present invention, the oxygen partial pressure under atmospheric pressure is 1.0 × 10 －３０ This is a process for obtaining a lithium-lanthanum-zirconium composite oxide powder by using a gas having a pressure of more than 1.0 atm and not more than 1.0 atm as a carrier gas, and heating the precursor powder dispersed in the carrier gas 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.

[0055] The oxygen partial pressure of the gas constituting the carrier gas under atmospheric pressure is 1.0 x 10 －３０ Atm to 1.0 atm or less is sufficient, but 1.0 x 10 －２５ ATM or higher 9.0×10 －１ atm or less, and 1.0 × 10 －２０ ATM or higher 8.0×10 －１ atm or less is more preferable, and 1.0 × 10 －１５ ATM or higher 7.0×10 －１ atm or less is more preferable, and 1.0×10 －１０ ATM or higher 6.0×10 －１ Atm or less is particularly preferred. By keeping the oxygen partial pressure within this range, the generation of oxygen vacancies can be suppressed while also suppressing the scattering of Li, making it easier to produce LLZ powder. Furthermore, 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 mixtures thereof can be used. Furthermore, depending on the need for atmospheric control, reducing gases such as hydrogen, carbon monoxide, methane, and ammonia gas can be used. Note that the present invention does not necessarily have to be carried out "under atmospheric pressure," and can be carried out under any appropriate pressure.

[0056] 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 2.3×10 －２ atm or more and less than 1.0 atm, and preferably 1.0×10 －１ atm or more and less than 1.0 atm, and more preferably 2.0×10 －１ atm or more and less than 1.0 atm, and more preferably 3.0×10 －１ atm or more and less than 1.0 atm, and more preferably 3.0×10 －１ ATM or higher 9.0×10 －１ More preferably, it is 3.0×10 atm or less. －１ ATM or higher 8.0×10 －１ More preferably, it is 3.0×10 atm or less. －１ ATM or higher 7.0×10 －１This makes it easier for the components in the precursor powder to react, so the reaction progresses easily even in a short time, promoting the reaction to produce LLZ and making it easier to obtain the desired LLZ powder.

[0057] The precursor powder is supplied into a 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, such as a nozzle with a circular, polygonal, or slit-shaped cross section, a nozzle with a tapered tip, or a nozzle that is tapered halfway and widens at the opening.

[0058] 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, particles of the precursor powder may come into contact with each other in the gas phase, causing aggregation or coalescence, which may require pulverization and / or crushing in the third step or later. The concentration of the precursor powder in the gas phase may be determined appropriately based on the specifications of the manufacturing apparatus 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. Note that there is no particular lower limit for the concentration of the precursor powder in the gas phase, but from the viewpoint of manufacturing efficiency, it is preferably 0.001 g / L or more.

[0059] The heating temperature of the precursor powder in the third step may be from 900° C. to 1200° C., preferably from 950° C. to 1150° C., and particularly preferably from 1000° C. to 1100° C. If the heating temperature is in this range, the LLZ powder can be produced efficiently.

[0060] 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. A heating time within this range facilitates efficient production of the LLZ powder.

[0061] As a heating method, heating by radiant heat is preferred, but the precursor powder can also be heated by directly contacting it with a heat source. For heating by radiant heat, an electric furnace (electric heater) or the like can be used, or 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 of 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, heating by directly contacting it with a heat source is preferred. Alternatively, the precursor powder can be heated by contacting it with a heated high-temperature gas. Furthermore, heating by an appropriate combination of the above-mentioned heating methods can be used; for example, the precursor powder can be directly heated by a flame and then heated by radiant heat from an electric furnace.

[0062] 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 to 1.0 μm, more preferably 30 nm to 900 nm, more preferably 30 nm to 800 nm, more preferably 30 nm to 700 nm, more preferably 30 nm to 600 nm, more preferably 30 nm to 500 nm, more preferably 30 nm to 400 nm, more preferably 30 nm to 300 nm, more preferably 40 nm to 250 nm, even more preferably 50 nm to 200 nm, and particularly preferably 60 nm to 150 nm. 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 is after recovery in the fourth step described below, but since it can be easily reduced in particle size by a crushing treatment, it can also be further reduced in particle size by a crushing treatment as appropriate before use. 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 treatment.

[0063] [Step 4] Step 4 according to the present invention is a step of recovering the lithium-lanthanum-zirconium composite oxide powder obtained in Step 3. 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.

[0064] The manufacturing method of the present invention may include a cooling step after the third step and before the fourth step, and 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.

[0065] <LLZ powder of the present invention> In the manufacturing method of the present invention, even if microcracks occur on the surface of the precursor powder, no microcracks remain on the surface of the LLZ powder after heat treatment, and neither pulverization nor crushing of the obtained LLZ powder is required, so that LLZ powder with excellent storage stability can be obtained, despite its small particle size, with the activity of the powder surface minimized. Note that, depending on the manufacturing conditions, particles may sinter together, but even in this case, since the particles can be crushed with an extremely weak force, microcracks and the like are unlikely to occur on the surface of the LLZ powder after crushing, the activity of the powder surface can be minimized, and the storage stability can be improved.

[0066] 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.

[0067] The LLZ powder according to the present invention is subjected to XRD measurement using an XRD measuring device (manufactured by 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 the lithium-lanthanum-zirconium composite oxide and lanthanum zirconate, and the peak areas of each peak are measured. The ratio of the peak area of ​​the lithium-lanthanum-zirconium composite oxide to the total peak area is calculated; however, it is sufficient that the ratio is more than 50%, and 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. The main peak may be, for example, near 31° in the case of lithium-lanthanum-zirconium composite oxide, or near 29° in the case of lanthanum zirconate.

[0068] The lithium-lanthanum-zirconium composite oxide powder of the present invention can be identified by a viscosity change ratio of 1 obtained by the following "Method for Measuring Viscosity Change Ratio." The acrylic resin used in the method for measuring viscosity change ratio below can be, for example, 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. However, the viscosity change ratio may also be measured using other acrylic resins having similar physical properties. That is, for example, the viscosity change ratio can be measured using a methacrylic resin having 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.

[0069] <Method for measuring viscosity change ratio> 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 of 40,000 or more and 50,000 or less 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.

[0070] As described above, when a ceramic powder is mixed with a solvent to prepare a ceramic slurry and then pulverized using a media mill or the like with extremely strong force for a long period of time to reduce the particle size, numerous microcracks and highly active surfaces appear on the surface of the resulting ceramic powder, causing lithium components to leach 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 leached from the LLZ powder react with other materials, particularly resins, 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 indicator of the amount of defects present in the crystalline structure of the LLZ powder.

[0071] The lithium-lanthanum-zirconium composite oxide powder of the present invention preferably has a weight loss rate at 100°C as measured 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.

[0072] Furthermore, the lithium-lanthanum-zirconium composite oxide powder of the present invention preferably has a weight loss rate at 300°C, as measured by thermogravimetric analysis (air atmosphere, temperature increase 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.

[0073] The present invention will be explained in more detail below using examples, but the present invention is not limited to the following examples.

[0074] (Examples 1 to 6, Comparative Examples 1 to 5) First, a lanthanum zirconate powder as shown in Table 1 was prepared. Next, 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 and coated on the surface of the lanthanum zirconate powder. Next, the lanthanum zirconate powder coated with these compounds was calcined at 700°C, and then further subjected to a crushing treatment and / or a pulverizing treatment 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 a range of 800 nm to 1200 nm (Comparative Example 1), thereby obtaining a precursor powder. Next, using a vertical tubular container equipped with a nozzle at the top for spraying the powder, the precursor powder was poured into a tube with an opening cross-sectional area of ​​2 cm. ２The precursor powder was dispersed in a gas phase using a carrier gas (air in Examples 1 to 5 and Comparative Examples 1 to 4, a mixed gas of nitrogen and oxygen in Comparative Example 5, and pure oxygen in Example 6. The partial oxygen pressure in the gas under atmospheric pressure was as shown in Table 1) from a nozzle. The precursor powder dispersed in the gas phase was then passed through the above-mentioned vertical tubular container and heated at the temperature shown in Table 1 for the time shown in Table 1. An electric furnace was installed outside the vertical tubular container used for heating, and was set to maintain the above-mentioned temperature inside the tubular container. The powder obtained by heating was then cooled to 180°C while dispersed in the gas phase, and the cooled powder was recovered. No pulverization or crushing treatment was performed after heating. The obtained powder was evaluated using the methods described below. The results are shown in Table 1.

[0075] 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 higher than in Example 1, and evaluation was carried out by the method described below. The results are shown in Table 1.

[0076] Example 8 A powder was produced in the same manner as in Example 7, except that a crushing treatment was carried out after collection, and evaluation was carried out by the methods described below. The results are shown in Table 1.

[0077] Comparative Example 6 First, 78 nm lanthanum zirconate powder, lithium carbonate, and lanthanum oxide were mixed using a wet mill for 20 hours 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 and heated at 750°C for 10 hours using a batch-type electric furnace, and then cooled to obtain a product. The obtained product was then mixed with terpineol to prepare a slurry, which was then pulverized using a bead mill to obtain a powder. The obtained powder was evaluated using the methods described below. The results are shown in Table 1.

[0078] Example 9 A powder was produced in the same manner as in Example 1, except that a zirconium compound and a lanthanum compound were coprecipitated, the resulting coprecipitate was fired, and the resulting sintered lanthanum zirconate powder having an average particle size of 82 nm was pulverized. The powder was evaluated as described below. The results are shown in Table 1.

[0079] Example 10 A powder was produced in the same manner as in Example 1, except that a precursor powder was prepared by mixing lanthanum zirconate powder having an average particle size of 80 nm, lithium carbonate powder, and lanthanum hydroxide powder in a bead mill to cause the lithium carbonate powder and lanthanum hydroxide powder to adhere to the surface of the lanthanum zirconate powder. The results are shown in Table 1.

[0080] <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 and their particle sizes were measured. The cumulative 50% particle size on a number basis was calculated based on the particle sizes, and this was taken as the average particle size. The particle size measured was the diameter of a perfect circle having the same area as the projected area of ​​the particle.

[0081] (LLZ Production) XRD measurement was performed using an XRD measurement device (Rigaku Corporation, SmartLab) with CuKα radiation (wavelength λ: 1.5418 Å) at 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, covering a diffraction angle 2θ of 10° to 90°. For lithium-lanthanum-zirconium composite oxide and lanthanum zirconate, the main peaks with the maximum peak intensity were detected, the peak areas of each peak were measured, and the ratio of the peak area of ​​the lithium-lanthanum-zirconium composite oxide to the total peak area was calculated. A ratio of more than 50% was designated "A," and a ratio of less than 50% was designated "B." Note that the main peak used was one near 31° for lithium-lanthanum-zirconium composite oxide, and one near 29° for lanthanum zirconate.

[0082] (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. under 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 ratio. The viscosity change ratio was rounded to 1 and was designated "A," and the viscosity change ratio was designated "B." The paste composition was stored in a sealed container at 25° C. until the viscosity was measured one week after preparation.

[0083]

[0084] 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 also be used for various purposes, such as materials for electronic components such as capacitors.

Claims

1. A method for producing a precursor powder by depositing the lanthanum compound and the lithium compound on the surface of the lanthanum zirconate powder in a first step and a second step of producing a precursor powder by depositing the lanthanum compound and the lithium compound on the surface of the lanthanum zirconate powder in a second step and ... －３０ 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 1,200° C. or less for a time of 1 second or more and 30 seconds or less in a state where the precursor powder is dispersed in the carrier gas, thereby obtaining 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.

2. A method for producing a lithium-lanthanum-zirconium composite oxide powder according to claim 1, wherein 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.

3. A method for producing a lithium-lanthanum-zirconium composite oxide powder according to claim 1, wherein 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.

4. A 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.

5. A 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 with the lanthanum compound and the 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 or more and 300 nm or less.

6. 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.

7. 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 ratio measured by the following method of 1. <Method of measuring viscosity change ratio> 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, and 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.