Solid electrolyte powder

Abstract

To provide a solid electrolyte powder that can be sintered at a relatively low temperature and can exhibit relatively high ionic conductivity under severe conditions.SOLUTION: The solid electrolyte powder of the present invention contains an oxide-based inorganic solid electrolyte material, has a BET specific surface area of 1.0 m2 / g to 100 m2 / g, and has a distribution constant n of 1.7 or more in the Rosin-Rammler equation: R=100exp(-bDn) (where D is the particle diameter, b is a particle size characteristic coefficient, and R is the percentage of particles larger than the particle diameter D relative to the total number of particles).SELECTED DRAWING: None

Description

Technical Field

[0001] This invention relates to a solid electrolyte powder containing an oxide-based inorganic solid electrolyte material.

Background Art

[0002] Among secondary batteries, in particular, all-solid-state batteries such as all-solid-state lithium-ion batteries in which the electrolyte is solid, compared to lithium-ion batteries using a liquid electrolyte, have excellent stability and reliability, high energy density, high output, and the possibility of realizing a wide operating temperature range, etc. Therefore, all-solid-state batteries are expected to be put into practical use in various applications such as automobiles, electronic devices, and household storage batteries.

[0003] All-solid-state batteries are generally roughly classified into a thin film type manufactured by a vapor phase method and a bulk type manufactured by sintering fine particles. Among these, the bulk type of all-solid-state battery is formed by laminating a powdery positive electrode active material, a solid electrolyte powder, and a powdery negative electrode active material between current collectors and sintering them. The solid electrolyte of the bulk type of all-solid-state battery is generally obtained by sintering the solid electrolyte powder during or prior to the manufacture of the all-solid-state battery, and is sometimes referred to as a sintered solid electrolyte.

[0004] Although various materials have been proposed as candidates for the material used for the sintered solid electrolyte, the selection of the material is important because it greatly affects the battery performance. Among them, among the oxide-based inorganic solid electrolyte materials, a composite oxide represented by A 2 / 3-x Li 3x TiO3 (0 < x < 0.16, A: one or more elements selected from lanthanoids), particularly a composite oxide having a perovskite crystal structure with A being La (so-called LLTO (registered trademark)) is regarded as promising because of its high ionic conductivity, stability, and durability, etc.

[0005] As related technologies, Patent Document 1 discloses "a ceramic raw material powder comprising oxide-based solid electrolyte powder, wherein the solid electrolyte powder has a D10% particle diameter of 0.05 μm or more and 0.6 μm or less, a D50% particle diameter of 0.08 μm or more and 1.5 μm or less, a D90% particle diameter of 2 μm or more and 4 μm or less, and a BET value of 3 m 2 / g or more and 20 m 2 / g or less".

[0006] Further, Patent Document 2 discloses "an oxide-based solid electrolyte comprising a compound represented by the following general formula (I): A 2 / 3-x Li 3x TiO3 (I) (where x satisfies 0.04 < x < 0.14, and A is one or more elements selected from lanthanoids), having an average particle diameter D50 of 0.1 μm to 1.0 μm and a BET specific surface area of 5.0 m 2 / g to 100.0 m 2 / g".

[0007] Further, Patent Document 3 discloses "a secondary battery comprising a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode, wherein the positive electrode and the negative electrode contain first solid electrolyte particles, the solid electrolyte layer contains second solid electrolyte particles, and the particle diameter of the second solid electrolyte particles is larger than that of the first solid electrolyte particles".

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0009] The solid electrolyte powder used in the sintered solid electrolyte is required to be sintered at a low temperature so that unintended reactions do not occur, for example, between the positive electrode active material and the negative electrode active material, when heated.

[0010] Furthermore, after sintering, the solid electrolyte powder may be used in a high-temperature and high-humidity environment inside an all-solid-state battery, and it may be required to exhibit high ionic conductivity even under such harsh conditions. Patent Documents 1 to 3 do not consider at all how to increase ionic conductivity under harsh conditions.

[0011] The present invention addresses the above-mentioned problems, and its object is to provide a solid electrolyte powder that can be sintered at a relatively low temperature and exhibits relatively high ionic conductivity under severe conditions. [Means for solving the problem]

[0012] As a result of extensive research, the inventors have found that a solid electrolyte powder having a predetermined surface area and a uniform particle size distribution such that the distribution constant n of the Rosin-Rammler equation is equal to or greater than a predetermined value can be sintered at low temperatures and exhibits high ionic conductivity even under harsh conditions.

[0013] The solid electrolyte powder of the present invention contains an oxide-based inorganic solid electrolyte material, and has a BET specific surface area of 1.0 m 2 / g~100m 2 / g, and the distribution constant n of the Rosin-Rammler equation, represented by the following formula (I), is 1.7 or more. R=100exp(-bD n ) (I) (In the above formula (I), D is the particle diameter, b is the particle size characteristic coefficient, and R is the percentage of the number of particles larger than the particle diameter D relative to the total number of particles.)

[0014] The above solid electrolyte powder preferably has an average circularity of the solid electrolyte particles contained therein of 0.8 to 1.0.

[0015] The above solid electrolyte powder may contain an oxide represented by the following formula (II). A 2 / 3-x Li 3x TiO3 (II) (In the above formula (II), x satisfies 0.04 < x < 0.14, and A is one or more elements selected from lanthanoids.)

[0016] The above solid electrolyte powder preferably has a SPAN value of 3.5 or less.

Advantages of the Invention

[0017] According to the solid electrolyte powder of this invention, sintering can be performed at a relatively low temperature, and a relatively high ionic conductivity can be exhibited under harsh conditions.

Modes for Carrying Out the Invention

[0018] The embodiments of this invention will be described in detail below. The solid electrolyte powder of one embodiment of this invention contains an oxide-based inorganic solid electrolyte material, and from the viewpoint of realizing predetermined low-temperature sinterability and ionic conductivity, the BET specific surface area is 1.0 m 2 / g to 100 m 2 / g.

[0019] Further, the above solid electrolyte powder has a distribution constant n of the Rosin-Rammler (R-R) distribution formula (also referred to as the "Rosin-Rammler formula") of formula (I): R = 100 exp(-bD n ) of 1.7 or more. When the distribution constant n of the solid electrolyte powder in the Rosin-Rammler formula is relatively large as described above, it can be evaluated that the particle size distribution is uniform. As a result, the solid electrolyte powder can be sintered at a low temperature and can exhibit a relatively high ionic conductivity under harsh conditions.

[0020] (Composition) As long as the solid electrolyte powder contains an oxide-based inorganic solid electrolyte material, various materials can be used. Specifically, in addition to the oxide represented by the general formula (II) described later, Li 1+x Al x Ti 2-x (PO4)3 (LATP) or Li 1+x Al x Ge 2-x (PO4)3 (LAGP) and other NASICOM-type electrolytes, Li 2+2x Zn 1-x GeO4 and other LISICON-type electrolytes, Li7La3Zr2O 12 (LLZ) and other garnet-type electrolytes can be mentioned. Such inorganic solid electrolyte materials have high ionic conductivity and can be suitably used as the solid electrolyte of all-solid-state batteries.

[0021] Among them, the oxide-based inorganic solid electrolyte material contained in the solid electrolyte particles preferably contains an oxide represented by the general formula (II): A 2 / 3-x Li 3x TiO3 (0.04 < x < 0.14, A is one or more elements selected from lanthanoids) from the viewpoints of ionic conductivity and chemical stability. In particular, it is preferable that A in the general formula (II) is La and contains an oxide of La 2 / 3-x Li 3x TiO3 (0.04 < x < 0.14). The composite oxide with a perovskite crystal structure in which A in the general formula (II) is La is sometimes referred to as LLTO (registered trademark). For example, the general formula (II-a): La x Li 2-3x TiO 3-a SrTiO3, the general formula (II-b): La x Li 2-3x TiO 3-a La 0.5 K 0.5 TiO3, the general formula (II-c): La x Li 2-3x Ti 1-a M a O 3-a , or the general formula (II-d): Sr x-1.5a ​a Li 1.5-2x Ti 0.5 Ta 0.5 03 (in general formulas (Ia) to (II-d), x satisfies 0.55≦x≦0.59, a satisfies 0≦a≦0.2, and M is at least one selected from Al, Fe, and Ga), and the Al2O3 content is 0.35 wt % or less and the SiO2 content is 0.1 wt % or less.

[0022] The presence of the oxide represented by the general formula (II) in the solid electrolyte powder can be confirmed by subjecting the solid electrolyte powder to X-ray diffraction. In the X-ray diffraction method, the X-ray diffraction pattern of the solid electrolyte powder obtained using a PANalytical X'pert Pro or a device substantially equivalent thereto is compared with the ICDD database (PANalytical Example Database and PDF-4+ 2019RDB) to identify the oxide represented by the general formula (II) contained in the solid electrolyte powder.

[0023] Here, the X-ray diffraction pattern of the solid electrolyte powder obtained by X-ray diffraction and from which noise has been removed is compared with the ICDD database, and if it is determined that the X-ray diffraction pattern of the oxide represented by general formula (II) is present in the X-ray diffraction pattern of the solid electrolyte powder, it is determined that the solid electrolyte powder contains the oxide represented by general formula (II).On the other hand, if it is determined that the X-ray diffraction pattern of the solid electrolyte powder is not present in the X-ray diffraction pattern of the solid electrolyte powder, it is determined that the solid electrolyte powder does not contain the oxide represented by general formula (II).

[0024] The oxide of general formula (II) contained in the solid electrolyte powder may have some of its oxygen atoms substituted with other elements such as F or Cl, or some of its transition metal atoms substituted with other metals such as Fe, Cr, Ti, Nb, W, Mo, Na, K, Mg, or Ca. Furthermore, the oxide of general formula (II) may have an excess or deficiency of Li or oxygen relative to the stoichiometric composition. Furthermore, the crystal structure of the oxide of general formula (II) contained in the solid electrolyte powder may be distorted. Even when a constituent element is substituted, deficient, or excessive relative to the stoichiometric composition of the oxide, or when the crystal structure is distorted, the oxide is still acceptable as the oxide of general formula (II) as long as the properties of the solid electrolyte powder are not altered.

[0025] When the X-ray diffraction patterns of oxides lacking constituent elements or oxides with excess constituent elements are compared with the ICDD database, there is a possibility that the peaks will shift from the X-ray diffraction pattern of the oxide represented by general formula (II). If such a peak shift is within ±10% of the reference value in the ICDD database, it is determined that the solid electrolyte powder contains the oxide represented by general formula (II).

[0026] The solid electrolyte powder preferably contains 99.0% by mass or more of the oxide represented by the general formula (II), and even more preferably 99.5% by mass or more. The higher the oxide content, the more desirable it is. There is no particular upper limit, but it may be, for example, 99.999% by mass or less, typically 99.99% by mass or less. The oxide content is measured by ICP (Inductively Coupled Plasma).

[0027] The solid electrolyte powder may contain, in addition to the oxide represented by the general formula (II), at least one impurity selected from the group consisting of Si, Al, and Fe. The content of the impurities in the solid electrolyte powder is preferably 1.0 mass% or less, more preferably 0.5 mass% or less.

[0028] (particle size distribution) The solid electrolyte powder according to the present invention has a distribution constant n of 1.7 or more in the Rosin-Rammler equation (I). If the distribution constant n is smaller than this, the particle diameters of the primary particles, in particular, are irregular, resulting in an uneven particle size distribution, and the density of the sintered body is reduced. As a result, the sintering temperature becomes higher, and the ionic conductivity may decrease under harsh conditions after sintering.

[0029] From the viewpoint of low-temperature sintering and improving ion conductivity under severe conditions, the distribution constant n is preferably 1.7 or more, and more preferably 1.8 or more. There is no particular disadvantage in that the distribution constant n is too large.

[0030] The Rosin-Rammler equation is given by: R = 100 exp(-bD n ) in the formula (I), D means particle diameter, b means particle size characteristic coefficient, and R means the percentage of the number of particles larger than particle diameter D to the total number of particles. Both n and b are parameters that depend on the powder. The Rosin-Rammler formula (I) is expressed as b = D e -n Let us consider the formula (III): R = exp{-(D / D e ) n D in this formula (III) can be rewritten as e is sometimes referred to as the particle size characteristic coefficient.

[0031] From the above formula (III), the formula (IV) is obtained: log{log(100 / R)}=nlogD+C, where C=log(loge)-nlogD e If the above formula (IV) is plotted on a graph with logD on the x-axis and log{log(100 / R)} on the y-axis, the plot on the graph will be an approximately straight line. This can be called a Rosin-Rammler diagram, and from this Rosin-Rammler diagram, a distribution constant equivalent to the gradient of the line can be determined by linear approximation using the least squares method. The larger the distribution constant n, the narrower the particle size range and the more uniform the particle sizes, which can be evaluated as indicating excellent particle size uniformity.

[0032] The particle diameter D, which is necessary to plot a Rosin-Rammler diagram to determine the distribution constant n, and the percentage R, which is the number of particles larger than particle diameter D relative to the total number of particles, are values obtained by laser diffraction, as will be described in detail later.

[0033] (particle size) The solid electrolyte powder has a 10% particle size D10 of 0.04 μm to 1.00 μm, a 90% particle size D90 of 3.50 μm or less, and a SPAN value of 3.5 or less.

[0034] If the 10% particle size D10 of the solid electrolyte powder is too small, the cohesive force increases, which may make pulverization difficult. On the other hand, if it is too large, the low-temperature sinterability may decrease. If the 90% particle size D90 is too large, the low-temperature sinterability may decrease. If the SPAN value is too large, the crystal grain size may vary, increasing the grain boundary contact area and resulting in low ionic conductivity. From this perspective, it is preferable that the 10% particle size D10 of the solid electrolyte powder be 0.04 μm to 1.00 μm, the 90% particle size D90 be 3.50 μm or less, and the SPAN value be 3.5 or less.

[0035] The particle size of the solid electrolyte powder can be measured using a laser diffraction / scattering particle size distribution analyzer LA-960 (manufactured by Horiba, Ltd.) or an equivalent measuring device. The solid electrolyte powder or solid electrolyte slurry is added to the measuring device so that the transmittance is approximately 80%, and the volume distribution is measured at a refractive index of 1.80 while applying ultrasound. The 10% particle size D10, 50% particle size D50, and 90% particle size D90 can be determined from the volume distribution.

[0036] The SPAN value can be calculated from the 10% particle diameter D10, the 50% particle diameter D50, and the 90% particle diameter D90 using the formula: SPAN value=(D90-D10) / D50.

[0037] (BET specific surface area) The BET specific surface area of the solid electrolyte powder is 1.0 m 2 / g~100m 2 / g.

[0038] If the BET specific surface area of the solid electrolyte powder is too small, it may not be possible to sinter it at a low temperature, whereas if the BET specific surface area is too large, the crystal grains may become small, increasing the contact area between the crystal grains and reducing the ionic conductivity.

[0039] The BET specific surface area of the solid electrolyte powder is measured by the BET method in accordance with JIS Z8830 (2013) after degassing at a degassing temperature of 140°C using a fully automatic specific surface area measuring device (Macsorb (registered trademark) manufactured by Mountech Co., Ltd. or a device substantially equivalent thereto).

[0040] (average circularity) The solid electrolyte particles constituting the solid electrolyte powder preferably have an average circularity of 0.8 to 1.0.

[0041] If the average circularity of the solid electrolyte particles is too small, the number of particles will be irregular, which may result in a decrease in density when molded.The average circularity is more preferably 0.82 to 1.00.

[0042] To determine the average circularity of solid electrolyte particles, 200 particles present in the field of view of an SEM image at a magnification that includes 200 to 300 particles are analyzed using image analysis software (public domain software "ImageJ" or software substantially equivalent thereto). Then, for each particle in the field of view, the perimeter B of a circle having an area equal to the area of the projection surface is divided by the perimeter A of the projection surface to determine the circularity (B / A), and the average value is taken as the average circularity.

[0043] (Manufacturing method) The above-described solid electrolyte powder can be produced, for example, by carrying out a raw material preparation step, a first wet-pulverization step, a calcination step, a second wet-pulverization step, and a crushing step in this order.

[0044] Here, it is particularly important not to perform dry pulverization. Dry pulverization generates coarse particles to a certain extent, and even if wet pulverization is subsequently performed, these coarse particles may remain, which may reduce the uniformity of the particle size distribution of the solid electrolyte powder. To achieve a uniform particle size distribution of the solid electrolyte powder, it is desirable to finely pulverize the particles by using a bead mill in the first wet pulverization step or by extending the pulverization time to achieve sufficient pulverization. Even if the pulverization time is extended in the first wet pulverization step, omitting dry pulverization can prevent the lead time of the entire manufacturing process from being prolonged.

[0045] An example of a method for producing a solid electrolyte powder will be described in detail below.

[0046] First, a raw material preparation step is performed in which lithium compounds such as lithium hydroxide and lithium carbonate are prepared as lithium raw materials, titanium compounds such as titanium oxide, metatitanic acid, and orthotitanic acid are prepared as titanium raw materials, and lanthanum oxide is prepared as a lanthanum raw material. If necessary, hydroxides, chlorides, and / or carbonates of at least one element selected from the group consisting of Sr, K, Fe, Ga, and Ta are also prepared.

[0047] In the raw material preparation step, it is important to prepare a titanium compound such as titanium oxide with a relatively small particle size as the titanium raw material. This makes it easier to adjust the particle size distribution or distribution constant n, particle size, and BET specific surface area of the solid electrolyte powder to be produced within the respective predetermined ranges. However, if the particle size of the titanium compound is too small, problems arise with handling. Specifically, the titanium compound such as titanium oxide preferably has a 10% particle size D10 of 1.1 μm to 1.2 μm, a 50% particle size D50 of 2.4 μm to 2.5 μm, a 90% particle size D90 of 4.6 μm to 4.9 μm, and a SPAN value of 1.44 to 1.49. Furthermore, the titanium compound used as the titanium raw material preferably has a BET specific surface area of 5.0 m 2 / g~100.0m 2 / g, more preferably 5.0m 2 / g~50.0m 2 / g. Also, the Rosin-Rammler equation (R = 100 exp(-bD n When the distribution constant n of the titanium compound (a) is calculated, the distribution constant n is preferably 2.18 to 2.22. By using a titanium compound with such a uniform particle size, the solid electrolyte powder produced therefrom also tends to have a uniform particle size. The particle size of the titanium compound can be measured using a laser diffraction / scattering particle size distribution analyzer LA-960 (manufactured by Horiba, Ltd.) or an equivalent measuring device. The titanium compound is added to the measuring device so that the transmittance is approximately 80%, and the volume distribution is measured at a refractive index of 2.50 while applying ultrasound. The 10% particle size D10, 50% particle size D50, and 90% particle size D90 are determined from the volume distribution. The SPAN value can be calculated from the 10% particle size D10, 50% particle size D50, and 90% particle size D90 using the formula: SPAN value = (D90 - D10) / D50. The BET specific surface area of the titanium compound is measured in the same manner as described above for the BET specific surface area of the solid electrolyte powder.

[0048] In the first wet-pulverization step, the raw materials, such as the lithium raw material, titanium raw material, and lanthanum raw material, prepared in the raw material preparation step, are mixed and pulverized in a predetermined molar ratio using a ball mill or a bead mill. Pure water and, if necessary, a dispersion medium such as an organic solvent such as ethanol are added to the ball mill, and the raw materials are pulverized in this state. When a bead mill is used in the first wet-pulverization step, the particles are made even finer than when a ball mill is used. This makes it easier to achieve a uniform particle size distribution in the solid electrolyte powder that is finally produced. Note that, taking into account the volatile content in the calcination step, the lithium raw material may be added in an amount 0 to 15% by weight more than the lithium amount in the desired composition.

[0049] When grinding using a ball mill, it is desirable to prevent the inclusion of Al2O3, SiO2, and other components of ball mills such as alumina-lined ball mills. Specifically, to shorten the time required for grinding and prevent the inclusion of ball mill components, grinding can be performed for, for example, 1 to 2 hours. Among ball mills, it is preferable to use a urethane-lined ball mill, a nylon ball mill, or a natural rubber-lined ball mill. Zirconia media and alumina media can be used as grinding media.

[0050] In the first wet-pulverization step, after pulverization, the mixture is dried using a spray dryer, fluidized bed dryer, tumbling granulation dryer, freeze dryer, hot air dryer, etc. When a spray dryer is used, the hot air inlet temperature is set to 200 to 250°C and the exhaust air temperature is set to 90 to 120°C, for example. This produces a first pulverized powder.

[0051] After the first wet-pulverization step, the first pulverized powder is subjected to a calcination step. In the calcination step, the first pulverized powder can be sieved using a sieve with a specified mesh size as needed, and then heated at 900°C to 1200°C for 1 hour to 12 hours in an oxygen or air atmosphere or an inert gas atmosphere such as nitrogen. After heating in the calcination step, the powder may be sieved using a sieve with a specified mesh size. This produces a calcined powder.

[0052] Next, a second wet-pulverization step is performed to wet-pulverize the calcined powder. In the second wet-pulverization step, it is desirable to first pulverize the calcined powder in a ball mill, and then pulverize the calcined powder multiple times in a bead mill, changing the size of the pulverization media as necessary. That is, the second wet-pulverization step involves pulverization two or more times using a ball mill and a bead mill. When pulverization is performed two or more times, the first pulverization is performed in a ball mill, and the second and subsequent pulverizations are performed multiple times in a bead mill. As a result, the particle size distribution of the solid electrolyte powder obtained ultimately tends to be sharper and the surface area tends to be adjusted to a predetermined value. However, depending on the size of the BET specific surface area of the solid electrolyte powder to be produced, pulverization using a ball mill or the like may be performed only once.

[0053] When grinding is performed twice or more times, the particle size of the grinding media used in the first grinding using a ball mill is preferably about 3 mm. The preferred particle size of the grinding media used in the second and subsequent grinding using a bead mill varies depending on the size of the BET specific surface area of the solid electrolyte powder to be produced. Regarding the particle size of the grinding media used in the second and subsequent grinding, the BET specific surface area of the solid electrolyte powder is preferably about 25 m. 2 / g, the particle diameter is preferably about 0.1 mm, and the BET specific surface area is about 50 m 2 / g, the particle diameter is preferably about 0.05 mm, and the BET specific surface area is preferably 60 m 2 / g or more (for example, about 80m 2 When the BET specific surface area is 60 m / g, the particle diameter is preferably about 0.05 mm. 2 / g or more (for example, about 80m 2 / g), it is preferable to set the heating temperature in the calcination step to a low temperature, for example, about 900°C. Note that for the first and second pulverization, bead mills with different types or structures of pulverization media as well as different sizes can be used.

[0054] The time for the first grinding is preferably within the range of 19 to 20 hours, and the time for the second and subsequent grinding is preferably within the range of 1 to 1.5 hours. By setting the grinding time for each grinding within the above ranges, it is possible to efficiently grind the material into particles of a predetermined particle size.

[0055] The ball mill or bead mill may have a drum with an inner lining of alumina, urethane, or natural rubber, or may be made of nylon. The grinding media may be made of zirconia or alumina.

[0056] In a ball mill or bead mill, a dispersant such as a surfactant and calcined powder are added to a solvent such as pure water to form a slurry, and the calcined powder is then pulverized in the slurry. When pulverization is performed multiple times, the second pulverization can be performed using the same solvent and dispersant without drying after the first pulverization.

[0057] Here, the slurry concentration, which is the ratio of the mass of the calcined powder to the mass of the slurry, is determined so that the BET specific surface area of the solid electrolyte powder to be produced is approximately 2 m 2 When the BET specific surface area of the solid electrolyte powder is 10 m / g, it is preferably 50 mass % to 60 mass %. 2 / g~80m 2 When the slurry concentration is set to 10% by mass / g, the slurry concentration is preferably 10% by mass to 30% by mass. If the slurry concentration is too high, the slurry viscosity increases and pulverization may become impossible. If the slurry concentration is too low, the solid content in the slurry is low, which may result in reduced productivity.

[0058] Furthermore, the dispersant concentration (ratio of the mass of the dispersant to the mass of the solvent) is preferably 0.5% by mass to 40% by mass, and even more preferably 1% by mass to 30% by mass. If the dispersant concentration is low, the particles may aggregate even after pulverization, resulting in a decrease in pulverization efficiency. If the dispersant concentration is too high, there is a concern that the ion conductivity may decrease due to residual carbon components. The larger the BET specific surface area of the solid electrolyte powder to be produced, the higher the dispersant concentration is preferably. For example, if the BET specific surface area of the solid electrolyte powder is 2m 2 / g~10m 2 / g, the dispersant concentration may be about 1 mass %, and the BET specific surface area of the solid electrolyte powder may be 30 m 2 / g~50m 2 / g, the dispersant concentration may be about 10 mass %, and the BET specific surface area of the solid electrolyte powder may be 60 m 2 / g or more, the dispersant concentration may be set to about 30% by mass.

[0059] After multiple rounds of pulverization are completed, the mixture is dried in the same manner as in the first wet pulverization step. A second pulverized powder is obtained by passing through the second wet pulverization step.

[0060] Thereafter, a crushing step may be carried out to crush the second crushed powder. When the crushing step is carried out, the second crushed powder is crushed to have a smaller particle size. In the crushing step, a dry jet mill, a ball mill, or the like may be used, but among them, a jet mill is preferred in terms of crushing efficiency.

[0061] After the above crushing step, the solid electrolyte powder as described above is obtained. [Example]

[0062] Next, a solid electrolyte powder according to the present invention was produced as a prototype, and its effects were confirmed. The following description will be given, however, for illustrative purposes only and is not intended to be limiting.

[0063] (Manufacturing method) The raw materials used were 36.0 g of lithium carbonate (manufactured by Sociedad Quimica y Minera de Chile SA, purity 99.2% by mass or higher), 290.6 g of lanthanum oxide (manufactured by Xuanxing New Wei Li Cheng Rare Earth Co., Ltd., purity 99.99% by mass or higher), and 250.0 g of titanium oxide (manufactured by Toho Titanium Co., Ltd., purity 99.99% by mass or higher). This titanium oxide had a 10% particle size D10 of 1.1 μm, a 50% particle size D50 of 2.4 μm, a 90% particle size D90 of 4.6 μm, a SPAN value of 1.49, and a Rosin-Rammler distribution constant n of approximately 2.18.

[0064] In Examples 1 to 4 and Comparative Example 1, the raw materials were weighed as the first pulverization, and then added to 1730.1 g of ion-exchanged water and 5 kg of alumina media (3 mm diameter) in a urethane-lined ball mill (5 L capacity), where pulverization was carried out for 5.5 hours. In Example 5, after this pulverization, pulverization was carried out for 1 hour in a bead mill using 0.3 mm diameter media, for a total of two pulverizations. In all of Examples 1 to 5 and Comparative Example 1, after pulverization, the material was dried using a spray dryer to obtain a first pulverized powder. Drying conditions were as follows: raw material supply rate: 10 to 30 L / h, hot air inlet temperature: 200 to 250°C, and exhaust air temperature: 90 to 120°C.

[0065] Next, the first pulverized powder was placed in a cordierite-mullite sagger and calcined in an electric furnace. The calcination conditions were an air atmosphere, a calcination time of 2 hours, and a calcination temperature of 1150°C in Examples 1 to 4 and Comparative Example 1, and 900°C in Example 5.

[0066] Thereafter, 0.55 kg of the calcined powder obtained by the calcination was subjected to wet milling once, twice, or three times as shown in Table 1 in Examples 1 to 5. The first milling was carried out for 19 or 15 hours using a ball mill (Nylon Pot NPN-5 manufactured by AS ONE Corporation) and 5 kg of 3 mm diameter zirconia milling media. The second milling was carried out for 1 hour using a bead mill (MiniCer manufactured by Ashizawa Finetech Co., Ltd.) and 520 g of 0.1 to 0.3 mm diameter zirconia milling media. The third milling was carried out for 1 hour using a bead mill (Ultra Apex Mill manufactured by Hiroshima Metal & Machinery Co., Ltd.) and 520 g of 0.05 mm diameter zirconia milling media. In addition to the milling media, 1650 g of ion-exchanged water and ammonium polyacrylate salt as a dispersant were added to the ball mill and bead mill. In Examples 1 to 5 and Comparative Example 1, the amounts of calcined powder and ammonium polyacrylate added were changed, and the slurry concentration and dispersant concentration were changed as shown in Table 1.

[0067] After the above pulverization, the mixture was dried using a spray dryer to obtain a second pulverized powder. Drying was performed under the following conditions: raw material supply rate: 10 to 30 L / h, hot air inlet temperature: 200 to 250°C, and exhaust air temperature: 90 to 120°C.

[0068] The second pulverized powder was then pulverized using a jet mill (STJ-200 manufactured by Seishin Enterprise Co., Ltd.). The conditions for pulverization using the jet mill were a throughput of 11 kg / hr, a pressure of 0.7 MPa, and a gliding pressure of 0.7 MPa. This resulted in the production of solid electrolyte powders for Examples 1 to 5 and Comparative Example 1.

[0069] [Table 1]

[0070] (evaluation) The solid electrolyte powders produced as described above were subjected to powder X-ray diffraction using PANalytical X'pert Pro, and the X-ray diffraction patterns obtained were compared with the ICDD database (PANalytical Example Database and PDF-4+ 2019RDB). As a result, the X-ray diffraction pattern of the compound represented by the general formula (II) was present in the X-ray diffraction pattern of each solid electrolyte powder, indicating that La 0.57 Li 0.29 It was confirmed that TiO3 was contained.

[0071] The 10% particle size D10, 50% particle size D50, 90% particle size D90, SPAN value, distribution constant n of the Rosin-Rammler equation, and average circularity of each of the solid electrolyte powders of Examples 1 to 5 and Comparative Example 1 were determined by the methods described above, and the results are shown in Table 2.

[0072] Furthermore, the sintering temperature was measured for each of the solid electrolyte powders of Examples 1 to 5 and Comparative Example 1 as follows. Uniaxial compression and cold isostatic pressing (CIP) were performed on the solid electrolyte powder in this order to obtain a compact. Specifically, a uniaxial compression apparatus (ESE-433-00 manufactured by ENERPAC) was used to perform uniaxial compression of 40 MPa on 0.5 g of solid electrolyte powder to produce a green compact. This green compact was then placed in a cold isostatic pressing apparatus (CPP28-300B manufactured by NPA Systems Corporation), and cold isostatic pressing (CIP) was performed on the green compact at a pressure of 200 MPa. This resulted in a cylindrical green compact with a diameter of 5 mm and a length of 10 mm.

[0073] The compact was then heated in air at a heating rate of 5°C / min using a thermomechanical analyzer (TMA, TMA8310, manufactured by Rigaku Corporation). This resulted in a graph showing the relationship between temperature and deformation ratio. The deformation ratio here refers to the percentage (%) of the ratio (ΔL / L1) of the difference ΔL (= L1-L2) between the length of the particles in contact with each other before sintering (L1) and the length of the particles in contact with each other after sintering (L2), relative to the length of the particles in contact with each other before sintering (L1). A differential curve of the TMA curve was obtained from this graph, and the position where the inflection point of the differential curve occurred was taken as the sintering temperature. The results are shown in Table 2.

[0074] In addition, sintered bodies were fabricated from the solid electrolyte powder after normal storage and storage under severe conditions, and their ionic conductivity was measured. For normal storage, 20 g of the solid electrolyte powder was spread on a stainless steel pad and left to stand at room temperature and normal pressure for 24 hours, after which a sintered body was fabricated as described below. For storage under severe conditions, 20 g of the solid electrolyte powder was spread on a stainless steel pad and left to stand in a constant temperature and humidity bath (IG-42H, manufactured by Yamato Chemical Co., Ltd.) at 50°C and 90% relative humidity for 24 hours, after which a sintered body was fabricated in the same manner.

[0075] After each storage, 0.59 g of the solid electrolyte powder was deaerated for 30 seconds at 0.1 ton, and then uniaxially compressed for 60 seconds at 2.26 ton to produce a disk-shaped green compact with a diameter of 12 mm and a thickness of 1.5 mm. This green compact was then heated at 1400°C for 6 hours to produce a sintered compact.

[0076] The ionic conductivity (lithium ion conductivity) of the above sintered body was measured as follows. Pt was vapor-deposited on both sides of a sintered body plate (Φ12 mm). The sides of the sintered body plate were first covered with masking tape or similar, and then Pt was vapor-deposited on both sides of the plate using an MC1000 ion sputtering machine manufactured by Hitachi High-Technologies Corporation at a current of 15 mA for 30 seconds. The plate was then sandwiched between stainless steel electrodes. A Nyquist plot was then measured at frequencies between 5 and 13 MHz, and the resistance values within the grains and at the grain boundaries were read from the measurement data. The lithium ion conductivity was calculated using the following formula. The results are shown in Table 2. Lithium ion conductivity (Scm -1 )=1 / (Rb+Rgb)×(L / S) Rb: Resistance value within the grain (Ω) Rgb: Resistance of grain boundary (Ω) L: Thickness of the plate-shaped lithium lanthanum titanium oxide (cm) S: electrode area (cm 2 )

[0077] [Table 2]

[0078] The solid electrolyte powders of Examples 1 to 5 all had a relatively large distribution constant n of the Rosin-Rammler equation, and had higher lithium ion conductivities after normal storage and storage under severe conditions than the solid electrolyte powder of Comparative Example 1, which had a small distribution constant n. Furthermore, the solid electrolyte powders of Examples 1 to 5 had lower sintering temperatures than the solid electrolyte powder of Comparative Example 1.

[0079] From the above, it is suggested that the solid electrolyte powder of the present invention may be sintered at a relatively low temperature and may exhibit relatively high ionic conductivity under severe conditions.

Claims

1. A solid electrolyte powder containing an oxide-based inorganic solid electrolyte material, BET specific surface area is 1.0 m 2 / g to 100m 2 / g, and the distribution constant n of the Rosin-Rammler equation represented by the following formula (I) is 1.7 or more. R=100exp(-bD n ) (I) (In the above formula (I), D is the particle diameter, b is the particle size characteristic coefficient, and R is the percentage of the number of particles larger than the particle diameter D relative to the total number of particles.)

2. 2. The solid electrolyte powder according to claim 1, wherein the solid electrolyte particles constituting the solid electrolyte powder have an average circularity of 0.8 to 1.

0.

3. 3. The solid electrolyte powder according to claim 1, which contains an oxide represented by the following formula (II): A 2 / 3-x Li 3x TiO 3 (II) (In the above formula (II), x satisfies 0.04<x<0.14, and A is one or more elements selected from the lanthanoids.)

4. 3. The solid electrolyte powder according to claim 1, wherein the SPAN value is 3.5 or less.

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