Lithium conductive sheet and manufacturing method thereof

Abstract

To provide a lithium conductive sheet capable of improving recovery efficiency of lithium from a liquid, and a manufacturing method thereof.SOLUTION: A lithium conductive sheet has a composition of Li3XLa2 / 3-XTiO3 (X is 0.05 or over and 0.3 or under), an area of a principal plane of 20 cm2 or over, a thickness of 10 μm or over and 1,000 μm or under, a strain ratio when seen from a direction in which a principal plane is extended of 10 or under, an average value of measurement results of lithium ion conductivity of randomly selected 50 points of 3.0×10-4S / cm or over, and a standard deviation of the measurement results of 1.0×10-4S / cm or under.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a lithium conductive sheet and a method for producing the same. [Background technology]

[0002] Lithium (Li) is widely used, for example, as a material for secondary batteries in mobile devices, vehicles, and the like. Demand for lithium is increasing every year, and in addition to methods for extracting lithium from ores, methods for efficiently recovering lithium from seawater, salt lake brine, and the like are being investigated (see, for example, Patent Document 1). In the latter method, for example, the use of a sheet formed from a sintered body capable of conducting lithium ions is being investigated (see, for example, Patent Document 2). Patent Document 2 listed below discloses a method for producing a lithium-lanthanum-titanium oxide sintered body that can be used as a solid electrolyte layer. In Patent Document 2 listed below, a mixed powder material is subjected to a calcination step, a pulverization step, a molding step, and a sintering step, in that order. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-131863 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-24725 Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-mentioned method for recovering lithium from a liquid, further improvement in efficiency on a practical scale is desired.

[0005] An object of one aspect of the present invention is to provide a lithium conductive sheet that can improve the efficiency of recovering lithium from a liquid, and a method for producing the same. [Means for solving the problem]

[0006] In view of the above circumstances, the present inventors have conducted extensive research and have completed the inventions set forth in the following items [1] to

[10] . [1] The composition is Li 3X La 2 / 3-X TiO3 (X is 0.05 or more and 0.3 or less), The area of ​​the main surface is 20 cm 2 That's all, The thickness is 10 μm or more and 1000 μm or less, The distortion rate when viewed from the extending direction of the main surface is 10 or less, The average lithium ion conductivity measured at 50 randomly selected locations was 3.0 × 10 -4 S / cm or more, and the standard deviation of the measurement results is 1.0 × 10 -4 A lithium conductive sheet having a conductivity of 0.1 S / cm or less. [2] The lithium conductive sheet according to [1], wherein X is 0.1 or more and 0.3 or less. [3] The lithium conductive sheet according to [1] or [2], wherein the strain rate is 7 or less. [4] The lithium conductive sheet according to any one of [1] to [3], wherein the distortion rate is the area of ​​a portion of the main surface, when placed on a horizontal surface, that is at least six times the thickness away from the horizontal surface, divided by the area of ​​the main surface. [5] A first step of forming a green sheet by drying a coating of a slurry containing oxides containing lanthanum, titanium, and lithium; a second step of preparing a plurality of green sheets and then supplying powder having an average particle size of 0.1 μm or more and 700 μm or less onto each main surface of the plurality of green sheets; a third step of forming a laminate by stacking a plurality of green sheets after the second step; a fourth step of firing the laminate; A method for manufacturing a lithium conductive sheet comprising the steps of: [6] The method for producing a lithium conductive sheet according to [5], wherein the first step uses a slurry produced by wet mixing a lanthanum raw material, a titanium raw material, a lithium raw material, a binder, and a solvent. [7] The method for producing a lithium conductive sheet according to [5], wherein the first step uses a slurry produced by wet mixing an oxide raw material containing lanthanum, titanium, and lithium with a binder and a solvent. [8] The method for producing a lithium conductive sheet according to any one of [5] to [7], wherein the powder contains 60 mass % or more of an oxide powder containing lanthanum, titanium, and lithium. [9] In the second step, the amount of powder supplied is 0.01 mg / cm 2 More than 10mg / cm 2 The method for producing a lithium conductive sheet according to any one of [5] to [8], which is as follows:

[10] The method for producing a lithium conductive sheet according to any one of [5] to [9], wherein the laminate is not pressurized in the third and fourth steps. [Effects of the Invention]

[0007] According to one aspect of the present invention, it is possible to provide a lithium conductive sheet that can improve the efficiency of recovering lithium from a liquid, and a method for producing the same. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic cross-sectional view showing a lithium conductive sheet according to an embodiment. [Figure 2] FIG. 2 is a schematic diagram illustrating a method for measuring the distortion rate of a lithium conductive sheet. [Figure 3] FIG. 3 is a schematic diagram of an example of a lithium recovery device using a lithium conductive sheet. [Figure 4] 4(a) and (b) are diagrams illustrating a method for producing a lithium conductive sheet according to an embodiment. [Figure 5] FIG. 5 is a diagram illustrating a method for producing a lithium conductive sheet according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment according to one aspect of the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same or equivalent elements are designated by the same reference numerals, and redundant description will be omitted.

[0010] <Lithium conductive sheet> The lithium conductive sheet according to this embodiment is The composition is Li 3X La 2 / 3-X TiO3 (X is 0.05 or more and 0.3 or less), The area of ​​the main surface is 20 cm 2 That's all, The thickness is 10 μm or more and 1000 μm or less, The distortion rate when viewed from the extending direction of the main surface is 10 or less, The average lithium ion conductivity measured at 50 randomly selected locations was 3.0 × 10 -4 S / cm or more, and the standard deviation of the measurement results is 1.0 × 10 -4 S / cm or less.

[0011] This lithium conductive sheet, with its strain rate controlled to 10 or less, is less likely to break even when its thickness and main surface area satisfy the above-mentioned numerical ranges. By using such a lithium conductive sheet, the amount of liquid that can be treated per sheet can be increased, thereby improving the efficiency of lithium recovery from liquid. In addition, the average value and standard deviation of the measurement results of the lithium ion conductivity of the lithium conductive sheet satisfy the above-mentioned numerical ranges. Therefore, by using the lithium conductive sheet according to this embodiment, the lithium ion conductivity per unit area of ​​the sheet main surface can be suitably set. Therefore, by using the lithium conductive sheet according to this embodiment, the efficiency of lithium recovery from liquid can be suitably improved.

[0012] The lithium conductive sheet of this embodiment will be described in detail below.

[0013] FIG. 1 is a schematic cross-sectional view showing a lithium conductive sheet according to this embodiment. The lithium conductive sheet 1 shown in FIG. 1 is a porous inorganic sheet used to recover lithium from, for example, seawater, brine, or the like. The lithium conductive sheet 1 exhibits the function of selectively transmitting (conducting) lithium (lithium ions) contained in a liquid. When viewed in the thickness direction of the sheet, the lithium conductive sheet 1 has, for example, a rectangular shape, but is not limited thereto. From the viewpoint of sheet durability and lithium conductivity, the thickness of the lithium conductive sheet 1 is, for example, 10 μm or more and 1000 μm or less. When the thickness of the lithium conductive sheet 1 is 10 μm or more, the lithium conductive sheet 1 is less likely to be damaged. When the thickness of the lithium conductive sheet 1 is 1000 μm or less, the lithium conductive sheet 1 can exhibit its lithium permeability function well. The lithium conductive sheet 1 can also be used as a solid electrolyte. Hereinafter, viewing the sheet in the thickness direction corresponds to viewing it in a plan view.

[0014] The lithium conductive sheet 1 has a first main surface 1a and a second main surface 1b. The first main surface 1a and the second main surface 1b are surfaces located on opposite sides of the lithium conductive sheet 1 in the thickness direction, and have, for example, a rectangular or circular shape. From the viewpoint of efficient lithium permeation, a Li adsorption film or the like that adsorbs lithium ions may be formed on at least one of the first main surface 1a and the second main surface 1b. The Li adsorption film is a surface treatment film in which some of the elements contained in the lithium conductive sheet 1 are substituted with hydrogen. From the viewpoint of improving the efficiency of lithium recovery, the area of ​​each of the first main surface 1a and the second main surface 1b is set to 20 cm or less. 2 The area is 30cm 2 Over 40cm 2 More than 50cm 2 From the viewpoint of preventing damage to the lithium conductive sheet, the area of ​​each of the first main surface 1a and the second main surface 1b may be, for example, 1000 cm 2 The area is 950cm 2 Below, 900cm 2 Below, 800cm 2 The following is also acceptable.

[0015] When the lithium conductive sheet 1 is viewed from the direction in which the first principal surface 1a and the second principal surface 1b extend, the strain rate (%) of the lithium conductive sheet 1 is 10 or less. In this case, even if the thickness of the lithium conductive sheet 1 and the areas of the first principal surface 1a and the second principal surface 1b are within the above ranges, the lithium conductive sheet 1 is less likely to break. The strain rate may be 7 or less, 5 or less, or 3 or less. In these cases, the lithium conductive sheet 1 is less likely to break.

[0016] A method for measuring the strain rate of the lithium conductive sheet 1 according to this embodiment will be described below with reference to FIG. 2. FIG. 2 is a schematic diagram illustrating the method for measuring the strain rate of the lithium conductive sheet. First, as shown in FIG. 2, the lithium conductive sheet 1 is placed on the horizontal plane HF of the stage 5. At this time, the first main surface 1a faces the horizontal plane HF. Next, a portion of the first main surface 1a that is separated from the horizontal plane by a predetermined distance D or more is identified. This portion is designated as a deviation portion DP included in the region R1 indicated by the dashed line in FIG. 2. The deviation portion DP is identified using, for example, a laser displacement meter. Next, the area of ​​the portion of the first main surface 1a included in the deviation portion DP is calculated. The value obtained by dividing this area by the area of ​​the first main surface 1a is designated as the strain rate of the lithium conductive sheet 1. In this embodiment, the distance D corresponds to a length six times the thickness of the lithium conductive sheet 1, but is not limited thereto. The distance D may correspond to a length five times the thickness of the lithium conductive sheet 1, or may correspond to a length seven times the thickness of the lithium conductive sheet 1.

[0017] The material constituting the lithium conductive sheet 1 is, for example, a crystal containing at least Li. The crystal has, for example, a perovskite crystal structure. In this case, Li ions can easily move within the lithium conductive sheet 1. The Li ion conductivity of the lithium conductive sheet 1 is exhibited by the movement of Li ions in the electrolyte solution located around the lithium conductive sheet 1 between Li sites in the crystal. At this time, for example, Li hydrate ions cannot enter the Li sites, so it is Li ions (Li+ )

[0018] In this embodiment, the crystal containing at least Li is a crystal of a composite oxide containing lanthanum, titanium, and lithium. A specific example of the crystal containing at least Li is lithium lanthanum titanate (Li 3X La 2 / 3-X TiO3, x is 0.05 or more and 0.3 or less, or x is 0.1 or more and 0.3 or less) (hereinafter referred to as LLTO). When the lithium conductive sheet 1 is formed from LLTO, the composition of the lithium conductive sheet 1 is Li 3X La 2 / 3-X The lithium conductive sheet 1 can be considered to be TiO3. The crystal containing at least Li may further contain elements other than Li, Ti, and La (e.g., Na, K, Ca, Ba, Si, Pb, Sr, Pr, Nd, Sm, Gd, Dy, Y, Eu, Tb, Ce, Ag, Bi, Mg, Co, Ni, Cu, Cr, Fe, Ga, Gd, In, Sc, Ge, Hf, Mn, Pr, Sn, Tb, Zn, Zr, W, Ru, Nb, Ta, Al, etc.). Even when the lithium conductive sheet 1 is formed from LLTO, the lithium conductive sheet 1 may contain trace amounts of the above elements.

[0019] The lithium ion conductivity of the lithium conductive sheet 1 is 3.0 × 10 -4 S / cm or more. In this embodiment, the lithium ion conductivity of the lithium conductive sheet 1 corresponds to the average value of the lithium ion conductivity measurement results at 50 randomly selected points on the lithium conductive sheet 1. In addition, the standard deviation of the measurement results is 1.0 × 10 -4 S / cm or less. The smaller the standard deviation, the smaller the variation in performance of the lithium conductive sheet 1. The lithium ion conductivity of the lithium conductive sheet 1 is calculated from a Cole-Cole plot obtained using an impedance analyzer for a measurement sample in which the lithium conductive sheet 1 is sandwiched between filter papers soaked in an aqueous solution containing lithium and then sandwiched between metal pieces.

[0020] FIG. 3 is a schematic diagram of an example of a lithium recovery device using a lithium conductive sheet. As shown in FIG. 3, the example lithium recovery device 100 is similar to the device disclosed in Japanese Patent Application Laid-Open No. 2017-131863 and includes a treatment tank 101 that accommodates a lithium conductive sheet 1 and mesh electrodes 102 and 103 that sandwich the lithium conductive sheet 1. The lithium conductive sheet 1 is supported by, for example, the electrodes 102 and 103 and placed in the treatment tank 101. The treatment tank 101 is divided into two regions (a first region 101a and a second region 101b) by the lithium conductive sheet 1. The first region 101a accommodates an electrolyte solution L1 containing lithium ions, such as seawater. The second region 101b accommodates a recovery liquid L2 containing lithium ions extracted from the electrolyte solution L1 by the lithium conductive sheet 1. The electrode 102 is a conductive portion accommodated in the first region 101a, and the electrode 103 is a conductive portion accommodated in the second region 101b. The electrodes 102 and 103 are electrically connected to a power source (not shown).

[0021] Next, a brief description will be given of a lithium recovery method using the lithium recovery device 100. First, in the lithium recovery device 100, a voltage is applied to the electrodes 102 and 103 so that the electrode 102 serves as a positive electrode and the electrode 103 serves as a negative electrode. This causes lithium ions 110 to migrate within the lithium conductive sheet 1 toward the electrode 103, which functions as the negative electrode. As a result, the migrated lithium ions 110 are selectively accumulated in the recovery liquid L2. Lithium can then be recovered from the electrolyte solution L1 by extracting the lithium ions 110 (or elemental lithium, lithium compounds, etc.) from the recovery liquid L2. Note that if the electrolyte solution L1 contains metal ions 120 such as sodium ions, these metal ions 120 cannot migrate within the lithium conductive sheet 1. Therefore, even when a voltage is applied to the electrodes 102 and 103, the metal ions 120 remain in the electrolyte solution L1.

[0022] <Method for manufacturing lithium conductive sheet> The method for producing the lithium conductive sheet of the present embodiment includes the steps of: A first step of forming a green sheet by drying a coating of a slurry containing oxides containing lanthanum, titanium, and lithium; a second step of preparing a plurality of green sheets and then supplying powder having an average particle size of 0.1 μm or more and 700 μm or less onto each main surface of the plurality of green sheets; a third step of forming a laminate by stacking a plurality of green sheets after the second step; a fourth step of firing the laminate; Equipped with.

[0023] According to this manufacturing method, powder is supplied onto the main surfaces of each green sheet in the second step, and then the stack of green sheets is fired. This suppresses distortion of each lithium conductive sheet formed by firing, allowing for both thin and large lithium conductive sheets. Therefore, using the lithium conductive sheet manufactured by this manufacturing method makes it possible to improve the lithium ion permeation rate and increase the permeation area. Therefore, by implementing this manufacturing method, the amount of liquid that can be processed per sheet can be increased, thereby improving the efficiency of lithium recovery from liquid. The average particle size of the powder is the number-average secondary particle size (diameter of secondary particles). The average particle size can be measured, for example, using a laser microscope, and is preferably 1 μm to 600 μm, more preferably 5 μm to 500 μm, and particularly preferably 10 μm to 400 μm.

[0024] Hereinafter, the method for producing a lithium conductive sheet according to this embodiment will be described in detail with reference to Fig. 4 and Fig. 5. Fig. 4(a), (b) and Fig. 5 are diagrams for explaining the method for producing a lithium conductive sheet according to this embodiment.

[0025] (Green sheet molding) First, a coating of a slurry containing oxides including lithium, lanthanum, and titanium is dried to form a green sheet 10 shown in FIG. 4(a) (first step). In the first step, a slurry containing the oxides is produced. Next, the slurry is coated onto one side of a substrate film (not shown). For example, the slurry is coated by a blade coating method, a doctor blade method, or a roll coating method using a die coater or lip coater. Next, the coated slurry is dried and peeled off. For example, the slurry is dried at 100°C for 1 hour. Before peeling off the dried slurry, excess portions may be removed using, for example, a Thomson blade. This completes the green sheet 10, which is a molded product.

[0026] The green sheet 10 is a plate-like member having a substantially rectangular shape in a planar view. The green sheet 10 has a first main surface 10a and a second main surface 10b. The first main surface 10a and the second main surface 10b are surfaces located on opposite sides of the green sheet 10 in the thickness direction. The first main surface 10a is the contact surface that was in contact with the base film before the green sheet 10 was peeled from the base film. The first main surface 10a has a surface shape that conforms to the surface of the base film. The second main surface 10b is the exposed surface of the green sheet 10 before it was peeled from the base film. The second main surface 10b may have irregularities due to the raw material powder. Therefore, during molding of the green sheet 10, the surface roughness of the first main surface 10a tends to be smaller than the surface roughness of the second main surface 10b. The base film is, for example, a resin film such as a polyethylene terephthalate (PET) film. By using a long base film, a long green sheet can be formed. The size and thickness of the green sheet can be determined, for example, taking into consideration the size and thickness of the fired sheet and the shrinkage rate due to firing.

[0027] The oxide contained in the slurry is produced, for example, by pulverizing and mixing a lanthanum (La) raw material, a titanium (Ti) raw material, and a lithium (Li) raw material. In this embodiment, the oxide is LLTO powder. Hereinafter, a powder containing a lanthanum (La) raw material, a titanium (Ti) raw material, and a lithium (Li) raw material will also be referred to as raw material powder. In addition to the raw material powder, a sintering aid or the like may be mixed with the oxide. The sintering aid is, for example, boron. For example, the oxide may contain a composite oxide containing boron. In the oxide, the molar ratio of the lanthanum raw material to the titanium raw material (i.e., La raw material / Ti raw material) is, for example, 0.6 to 0.65, and the molar ratio of the lithium raw material to the titanium raw material (i.e., Li raw material / Ti raw material) is, for example, 0.15 to 0.5.

[0028] Lanthanum raw material is a powder primarily composed of lanthanum, such as lanthanum oxide, lanthanum carbonate, or lanthanum hydroxide. The lanthanum raw material may contain a single material or multiple materials. For example, the lanthanum raw material may contain only lanthanum oxide, or may contain both lanthanum oxide and lanthanum carbonate. The lanthanum raw material corresponds to a material with the highest lanthanum content. Therefore, the lanthanum raw material may contain elements other than La (e.g., Na, K, Ca, Ba, Si, Pb, Sr, Pr, Nd, Sm, Gd, Dy, Y, Eu, Tb, Ce, Ag, Bi, Mg, Co, Ni, Cu, Cr, Fe, Ga, Gd, In, Sc, Ge, Hf, Mn, Pr, Sn, Tb, Zn, Zr, W, Ru, Nb, Ta, Al, etc.). The lanthanum raw material may contain various impurities. For example, even if the lanthanum raw material is set to contain only lanthanum oxide, the lanthanum raw material may contain impurities. In this embodiment, lanthanum oxide (La2O3) is used as the lanthanum raw material.

[0029] The titanium raw material is a powder primarily composed of titanium. Examples of the titanium raw material include titanium oxide, titanium hydroxide, and various titanates. The titanium raw material may contain a single material or multiple materials. For example, the titanium raw material may contain only titanium oxide, or may contain titanium oxide and titanium hydroxide. The titanium raw material corresponds to the material with the highest titanium content. Therefore, like the lanthanum raw material, the titanium raw material may contain elements other than Ti. The titanium raw material may contain various impurities. For example, even if only titanium oxide is selected as the titanium raw material, the titanium raw material may contain impurities. From the perspective of cost reduction, titanium oxide may be used as the titanium raw material. In this case, either anatase titanium oxide (TiO2) or rutile titanium oxide (TiO2) may be used. In this embodiment, anatase titanium oxide (TiO2) is used as the titanium raw material.

[0030] The lithium raw material is a powder mainly composed of lithium, such as lithium oxide, lithium carbonate, or lithium hydroxide. The lithium raw material may contain a single material or multiple materials. For example, the lithium raw material may contain only lithium hydroxide, or may contain lithium hydroxide and lithium carbonate. The lithium raw material corresponds to the material with the highest lithium content. Therefore, the lithium raw material may contain elements other than Li, similar to the lanthanum raw material and titanium raw material. The lithium raw material may contain various impurities. For example, even if only lithium hydroxide is selected as the lithium raw material, the lithium raw material may contain impurities. In this embodiment, lithium oxide (LiO) is used as the lithium raw material.

[0031] The impurities are organic or inorganic substances other than the main constituent elements. Examples of impurities include oxides, chlorides, hydroxides, etc. containing at least one of Na, K, Ca, Ba, Pb, Sr, Pr, Nd, Sm, Gd, Dy, Y, Eu, Tb, Ce, Ag, Bi, Mg, Co, Ni, Cu, Cr, Fe, Ga, Gd, In, Sc, Ge, Hf, Mn, Pr, Sn, Tb, Zn, Zr, W, Ru, Nb, Ta, Al, and Y. The impurities can be identified and quantified, for example, by ICP analysis, as described in the Examples below, or by X-ray diffraction, as needed.

[0032] The measured raw materials are pulverized and mixed by a known method. For example, the raw materials may be pulverized and mixed using a known mixer / pulverizer. The mixer / pulverizer may be, for example, a medium-flow mixer / pulverizer (a ball mill, a planetary mill, etc.), an agitator mixer / pulverizer (a tower mill, an agitator / calculator mill, a flow pipe mill, etc.), or a mortar (an agate mortar, an alumina mortar, a mortar / mortar maker, etc.). The raw materials may be wet-mixed or dry-mixed. The measured raw materials may be mixed in a mixer such as a container rotary mixer (a horizontal cylinder, an inclined cylinder, a V-type, etc.) or a mechanical agitator mixer (a ribbon, a screw, a rod, etc.), and then pulverized in a mortar or the like.

[0033] In this embodiment, the measured lanthanum raw material, titanium raw material, and lithium raw material are wet-mixed in a ball mill to form a slurry without being calcined. In the wet mixing, a solvent is used to disperse each raw material. Additionally, after at least a binder is added during the wet mixing, the wet mixing is continued. Therefore, in this embodiment, a slurry is formed by wet-mixing the lanthanum raw material, titanium raw material, lithium raw material, binder, and solvent. This results in a slurry containing a pulverized mixture of each raw material. This slurry is then subjected to, for example, a degassing treatment. During the wet mixing, materials other than the raw material powder, solvent, and binder may be added. Note that in this embodiment, the solvent and binder are added sequentially to the raw material powder, but this is not a limitation. The solvent and binder may also be added to the raw material powder at the same time. The wet mixing is continued, for example, until all of the materials contained in the mixture are mixed.

[0034] The type of binder is not particularly limited, and may be appropriately selected from, for example, organic binders and inorganic binders that are known in conventional ceramic sheet manufacturing methods.

[0035] Examples of organic binders include ethylene copolymers, styrene copolymers, acrylate and methacrylate copolymers, vinyl acetate copolymers, maleic acid copolymers, vinyl acetal resins, vinyl formal resins, polyvinyl butyral resins, vinyl alcohol resins, celluloses such as ethyl cellulose, and waxes. Among these, from the viewpoints of formability and / or strength of the green sheet, and particularly thermal decomposition property when fired in large quantities for mass production, alkyl acrylates having an alkyl group of 10 or less carbon atoms, such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, isobutyl acrylate, cyclohexyl acrylate, and 2-ethylhexyl acrylate; alkyl methacrylates having an alkyl group of 20 or less carbon atoms, such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, isobutyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, and lauryl methacrylate; Preferred are acrylate and methacrylate copolymers obtained by polymerizing or copolymerizing at least one of the following: acrylates; hydroxyalkyl acrylates or hydroxyalkyl methacrylates having a hydroxyalkyl group, such as hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, and hydroxypropyl methacrylate; aminoalkyl acrylates or aminoalkyl methacrylates, such as dimethylaminoethyl acrylate and dimethylaminoethyl methacrylate; and carboxyl group-containing monomers, such as acrylic acid, methacrylic acid, maleic acid, and maleic acid half esters, such as monoisopropyl maleate. The number-average molecular weight (Mn) of the copolymer or resin contained in the organic binder is preferably 20,000 to 200,000, more preferably 30,000 to 100,000. The weight-average molecular weight (Mw) of the resin is preferably 100,000 to 1,000,000, more preferably 120,000 to 500,000. The dispersity (Mw / Mn) is preferably 1.0 or more and 5.0 or less, and more preferably 1.0 or more and 4.7 or less.The number average molecular weight and the weight average molecular weight are measured, for example, by gel permeation chromatography (GPC). These organic binders can be used alone or in combination of two or more types as needed. Particularly preferred are copolymers of monomers containing 60% by mass or more of n-butyl methacrylate and / or 2-ethylhexyl methacrylate.

[0036] As the inorganic binder, for example, at least one selected from zirconia sol, silica sol, alumina sol, titania sol, and the like can be used.

[0037] The mass ratio of the raw material powder to the binder in the slurry is not particularly limited. For example, the binder may be 5 parts by mass or more and 30 parts by mass or less, or 10 parts by mass or more and 20 parts by mass or less, relative to 100 parts by mass of the raw material powder. The content of the binder in the slurry is selected depending on the performance, such as strength and flexibility, required for the green sheet and / or the sintered lithium conductive sheet.

[0038] The type of solvent used in the slurry is not particularly limited. For example, it can be appropriately selected from solvents known in conventional ceramic sheet manufacturing methods. For example, a solvent appropriately selected from water; alcohols such as ethanol, 2-propanol, 1-butanol, and 1-hexanol; ketones such as acetone and 2-butanone; aliphatic hydrocarbons such as pentane, hexane, and heptane; aromatic hydrocarbons such as benzene, toluene, xylene, and ethylbenzene; and acetate esters such as methyl acetate, ethyl acetate, and butyl acetate can be used alone or in combination. The amount of solvent used is adjusted taking into account the viscosity of the slurry. In this embodiment, a mixed solvent of toluene and ethyl acetate is used as the solvent.

[0039] If necessary, dispersants, plasticizers, lubricants, surfactants, and / or antifoaming agents may be added to the slurry. For example, dispersants are added to promote deflocculation and / or dispersion of the ceramic raw material powder. Examples of dispersants include polymer electrolytes such as polyacrylic acid and ammonium polyacrylate; organic acids such as citric acid and tartaric acid; copolymers of isobutylene or styrene with maleic anhydride and their ammonium salts or amine salts; and copolymers of butadiene with maleic anhydride and their ammonium salts. For example, plasticizers are added to impart flexibility to the green sheet. Examples of plasticizers include phthalate esters such as dibutyl phthalate (dibutyl phthalate) and dioctyl phthalate; phthalate polyesters; glycols such as propylene glycol; glycol ethers; and the like.

[0040] (powder supply) After preparing a plurality of green sheets 10 to be formed in the first step, powder is supplied onto each of the main surfaces of the plurality of green sheets 10 (second step). In this embodiment, as shown in FIG. 4(b), in the second step, the powder 20 is attached to the second main surface 10b of each green sheet 10, but this is not limiting. The powder 20 may be attached to the first main surface 10a, or may be attached to both the first main surface 10a and the second main surface 10b. In the second step, the amount of powder 20 supplied per green sheet 10 varies depending on the size of the green sheet 10, but may be, for example, 0.01 mg / cm 2 More than 10mg / cm 2 In this case, the powder 20 is supplied to the entire second main surface 10b. Methods for supplying the powder 20 to the green sheet 10 include, for example, applying a liquid in which the powder 20 is dispersed onto the green sheet 10, and spraying the liquid in which the powder 20 is dispersed. The powder 20 is adhered irregularly onto the green sheet 10, but is not limited to this.

[0041] The powder 20 is used to prevent contact between the green sheets 10 in the laminate S (see FIG. 5 ), which will be described later. The shape of the powder 20 is not particularly limited and may be, for example, spherical. The average particle size of the powder 20 is 0.1 μm or more and 700 μm or less. This allows the sheets to be relatively easily peeled from each other after firing without reducing the bending strength of the lithium conductive sheet 1 to be manufactured later. The lower limit of the average particle size of the powder 20 may be 0.5 μm or more, 1 μm or more, or 1.5 μm or more. The upper limit of the average particle size of the powder 20 may be 300 μm or less, 200 μm or less, or 100 μm or less. In this specification, the average particle size of the powder 20 refers to the particle size (d50) corresponding to 50% cumulative volume, determined from the particle size distribution obtained by particle size distribution measurement using a laser diffraction method. The average particle size of the powder 20 can be measured using, for example, a laser diffraction / scattering particle size distribution measuring device LA-920 (manufactured by Horiba, Ltd.).

[0042] The powder 20 may be an organic or inorganic material. The powder 20 may include both organic and inorganic powders. From the viewpoints of yield, cost, and the like, an organic powder may be used as the powder 20. The organic powder may be, for example, a natural organic powder or a synthetic organic resin powder. Examples of natural organic powders include starch powders such as wheat flour, corn starch (cornstarch), sweet potato starch, potato starch, and tapioca starch. Examples of synthetic organic resin powders include sublimable resin powders such as melamine cyanurate. From the viewpoint of reliably preventing fusion between sheets, an inorganic powder may be used as the powder 20. Examples of inorganic powders include lanthanum raw materials, titanium raw materials, and lithium raw materials. Specific examples of inorganic powders include lanthanum oxide and titanium oxide. In these cases, even if the powder 20 is fused during the production of the lithium conductive sheet 1, the performance of the lithium conductive sheet 1 is less likely to deteriorate. From the viewpoint of suppressing deterioration in the performance of the lithium conductive sheet 1, the inorganic powder may contain an oxide powder containing lanthanum, titanium, and lithium. In this case, the powder 20 may contain 60% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more of the oxide powder. The more the oxide powder is contained in the powder 20, the less likely the performance of the lithium conductive sheet 1 will deteriorate, even if the powder 20 is fused to the lithium conductive sheet 1.

[0043] The inorganic powder may be either an LLTO powder or a LLTO powder. In other words, the inorganic powder may be either an LLTO powder or a companion material to the raw material powder used in the lithium conductive sheet 1. In this case, the mass ratio of the lanthanum raw material, the titanium raw material, and the lithium raw material in the inorganic powder may be different from the mass ratio of the lanthanum raw material, the titanium raw material, and the lithium raw material contained in the raw material powder of the lithium conductive sheet 1. In this embodiment, LLTO powder is used as the powder 20. As a result, even if the powder 20 is fused to the lithium conductive sheet 1, the powder 20 can be considered as part of the lithium conductive sheet 1 (not as an impurity), and therefore the performance of the lithium conductive sheet 1 is unlikely to deteriorate. Note that, if the powder 20 is fused to the lithium conductive sheet 1, the powder 20 may be removed by a known method.

[0044] (Laminate) After the second step, as shown in FIG. 5, a laminate S is formed by stacking a plurality of green sheets 10 (third step). In the third step, first, the green sheet 10 is placed on the mounting surface 50a of the setter 50. At this time, the green sheet 10 is placed on the setter 50 so that the main surface to which the powder 20 is attached is exposed. Next, another green sheet 10 is stacked on top of the green sheet 10 to form the laminate S. The laminate S includes, for example, two to ten green sheets 10. From the viewpoint of suppressing deformation of the green sheets 10, no pressure is applied to the laminate S in the third step.

[0045] The setter 50 is a heat-resistant member that supports the green sheet 10 and is made of, for example, aluminum oxide (alumina), titanium oxide, silicon oxide (silica), or a composite oxide thereof. From the viewpoints of cost and durability, the setter 50 may be an alumina setter containing alumina. In this case, the purity of the alumina in the setter 50 is, for example, 99% or more. The porosity of the setter 50 is, for example, 50% or less. To facilitate the release of the lithium conductive sheet 1 from the setter 50, at least a portion of the mounting surface 50a of the setter 50 contains an oxide containing at least one of lanthanum, titanium, and lithium. The oxide is, for example, lanthanum oxide, titanium oxide, lithium oxide, lanthanum-titanium oxide, lanthanum-lithium oxide, titanium-lithium oxide, or lanthanum-titanium-lithium oxide. When the setter 50 is an alumina setter, the oxide is formed by, for example, baking a powder containing at least one of a lanthanum raw material, a titanium raw material, and a lithium raw material onto the mounting surface 50a. Specifically, by heating the setter 50 on which the powder is placed on the placement surface 50a, the powder becomes part of the placement surface 50a. The powder is placed on the placement surface 50a using, for example, a sieve, a brush, or the like.

[0046] (Firing) After the third step, the laminate S is fired (fourth step). In the fourth step, each green sheet 10 included in the laminate S is first degreased. For example, each green sheet is degreased by increasing the temperature from room temperature to 500°C over 10 hours. Next, the degreased laminate S is fired to produce multiple lithium conductive sheets 1. For example, the green sheets 10 are fired at 1100°C to 1500°C using a known method such as an electric furnace, which is different from the equipment used for degreasing. Here, firing the green sheets in an electric furnace corresponds to maintaining the electric furnace in which the green sheets were fired at a predetermined temperature for a predetermined time. The green sheets 10 are fired, for example, in an air atmosphere or a low-oxygen atmosphere for 10 minutes to 6 hours. This removes organic components such as the binder and solvent, and forms composite oxide sheets (lithium conductive sheets) composed of oxides containing lanthanum, lithium, and titanium. The stacked sheets are then peeled off from each other to obtain multiple lithium conductive sheets 1. In this embodiment, the composite oxide has a perovskite crystal structure equivalent to LLTO obtained by calcining a lanthanum raw material, a titanium raw material, and a lithium raw material. Note that, in the fourth step, pressure is not applied to the laminate S in order to prevent deformation of the green sheet 10.

[0047] When the powder 20 contains an inorganic powder, at least a portion of the powder 20 may be fused to the lithium conductive sheet 1 after the fourth step. In this embodiment, the arithmetic surface roughness Ra of the second main surface 1b is preferably 1 μm or more and 50 μm or less, and more preferably 1 μm or more and 10 μm or less. In this case, the lithium separation efficiency can be improved as the surface area of ​​the second main surface 1b increases while maintaining the strength of the lithium conductive sheet 1. The arithmetic surface roughness Ra of the second main surface 1b may be 2 μm or more, 3 μm or more, 4 μm or more, 30 μm or less, 10 μm or less, or 5 μm or less. On the other hand, the arithmetic surface roughness Ra of the first main surface 1a in this embodiment is 0.1 μm or more and 0.8 μm or less. The arithmetic surface roughness Ra of the first principal surface 1a may be 0.2 μm or more, 0.3 μm or more, 0.7 μm or less, or 0.5 μm or less. The difference in arithmetic surface roughness Ra between the first principal surface 1a and the second principal surface 1b can be attributed to the powder 20. The arithmetic surface roughness of each principal surface is measured based on the contents of JIS B 0601:2013. The arithmetic surface roughness of each principal surface can be measured, for example, using a stylus-type surface roughness measuring instrument.

[0048] Next, the effects of the lithium conductive sheet 1 manufactured by the manufacturing method according to this embodiment will be described in comparison with a manufacturing method according to a reference example described below. In the manufacturing method according to the reference example, lithium conductive sheets are manufactured one by one without forming a laminate. In this reference example, for example, the green sheet is deformed by gas generated from the sheet during degreasing, resulting in a large distortion rate of the lithium conductive sheet. Therefore, in the reference example, if the green sheet is made large, the lithium conductive sheet easily breaks, making it difficult to put into practical use.

[0049] In contrast, according to the manufacturing method of this embodiment, the powder 20 is supplied onto the second main surface 10b of each green sheet 10 in the second step, and then the laminate S of the green sheets 10 is fired. By forming the laminate S in this manner, upward warping due to the sheet load is suppressed in all green sheets 10 except the uppermost one. Therefore, distortion of at least the lithium conductive sheets 1 other than the uppermost one is suppressed. Furthermore, due to the moderate fusion between the powder 20 and the green sheets 10, the shape of each lithium conductive sheet 1 tends to follow the shape of the other lithium conductive sheets 1 whose deformation is suppressed, so distortion of the uppermost lithium conductive sheet 1 is also suppressed. Therefore, by adopting the above manufacturing method, distortion of each lithium conductive sheet 1 formed by firing is suppressed, and the distortion rate can be controlled to 10 or less. Therefore, even when the thickness of the lithium conductive sheet 1 and the areas of the first main surface 10a and the second main surface 10b satisfy the above numerical ranges, breakage and the like are unlikely to occur. Additionally, in this embodiment, the average value and standard deviation of the measurement results of the lithium ion conductivity of the lithium conductive sheet 1 satisfy the above-mentioned numerical ranges. Therefore, by using the lithium conductive sheet 1 according to this embodiment, it is possible to satisfactorily set the lithium ion conductivity per unit area of ​​the lithium conductive sheet 1. As described above, by using the lithium conductive sheet 1 according to this embodiment, it is possible to satisfactorily improve the efficiency of lithium recovery from a liquid.

[0050] Furthermore, in this embodiment, by firing the laminate S, the difference between the composition of each lithium conductive sheet 1 and the composition of the raw material powder contained in the slurry tends to be smaller compared to the reference example (this can also be referred to as a tendency for the compositional difference between the lithium conductive sheet and the raw material powder in the slurry to be smaller). In particular, the difference between the proportion of lithium contained in each lithium conductive sheet 1 and the proportion of lithium contained in the slurry tends to be smaller compared to the reference example. Therefore, in this embodiment, it can be said that it is easier to produce a lithium conductive sheet 1 having the desired composition compared to the reference example. Note that in the laminate S, the lithium conductive sheets 1 farther from the setter 50 tend to have smaller compositional differences. Although this is not certain, it is thought that the lithium conductive sheets 1 farther from the setter 50 are more able to absorb lithium dispersed from other green sheets 10 during firing, etc. In addition, it is possible that the lithium conductive sheets 1 closest to the setter 50 absorb lithium into the setter 50 during firing. The composition difference corresponds to, for example, the difference between the lithium-lanthanum molar ratio contained in the lithium conductive sheet and the lithium-lanthanum molar ratio contained in the raw material powder in the slurry.

[0051] In this embodiment, the distortion rate of the lithium conductive sheet 1 may be equal to or less than 7. In this case, even if the thickness of the lithium conductive sheet 1 and the areas of the first main surface 10a and the second main surface 10b satisfy the above-mentioned numerical ranges, breakage and the like are unlikely to occur.

[0052] In this embodiment, the powder 20 may contain 60 mass % or more of an oxide powder containing lanthanum, titanium, and lithium. In this case, even if the powder 20 is fused to the lithium conductive sheet 1, the performance of the lithium conductive sheet 1 is unlikely to deteriorate.

[0053] In this embodiment, the amount of powder supplied in the second step is 0.01 mg / cm 2 More than 10mg / cm 2 This is because: After the fourth step, the lithium conductive sheets 1 are less likely to fuse together.

[0054] In this embodiment, the laminate S is not pressurized in the third and fourth steps. This prevents the green sheets 10 from coming into contact with each other before firing the laminate S, making it difficult for the lithium conductive sheets 1 to fuse together after the fourth step.

[0055] The above embodiment describes one aspect of the present invention. Therefore, the present invention is not limited to the above embodiment and can be modified. For example, in the above embodiment, a slurry produced by wet-mixing a lanthanum raw material, a titanium raw material, a lithium raw material, a binder, and a solvent is used in the first step. However, the present invention is not limited to this. For example, a slurry produced by wet-mixing an oxide raw material containing lanthanum, titanium, and lithium, a binder, and a solvent may be used in the first step. The oxide raw material is, for example, a mixture of a lanthanum raw material, a titanium raw material, and a lithium raw material. For example, the lanthanum raw material, the titanium raw material, and the lithium raw material are pulverized and mixed using a ball mill or the like to obtain the oxide raw material. Note that the raw materials do not need to be calcined when producing the oxide raw material. In this case, material costs can be reduced.

[0056] In the above embodiment, the excess portion is removed before peeling off the green sheet, which is the dried slurry. However, this is not limited to this. For example, the slurry may be applied to a mold placed on one side of the base film. In this case, the green sheet can be formed without removing the excess portion. [Example]

[0057] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0058] Example 1 (Green Sheet) Lanthanum oxide (manufactured by Kanto Chemical Co., Inc.), anatase-type titanium oxide (manufactured by Teika Corporation), and lithium carbonate (manufactured by Kishida Chemical Co., Ltd.) were prepared as raw material powders. Lanthanum oxide was placed in an alumina sagger, heated at 700°C for 1 hour, and dried. Subsequently, a total of 100 parts by mass of a mixed powder consisting of 50.4 parts by mass of lanthanum oxide, 43.6 parts by mass of titanium oxide, and 6.0 parts by mass of lithium carbonate was placed in a nylon mill loaded with zirconia balls. Here, not only the mixed powder but also 103.4 parts by mass of a mixed solution of a dispersant and a solvent was placed in the nylon mill. In the mixed solution, the dispersant was 3.7 parts by mass of a commercially available polycarboxylic acid ester-type polymer dispersant, and the solvent was a mixed solvent of toluene and ethyl acetate (solvent toluene mass:ethyl acetate mass = 1:1). Subsequently, the mixed powder and the mixed solution were milled for 20 hours. Next, a binder made of a methacrylic copolymer (manufactured by Nippon Shokubai Co., Ltd., number average molecular weight: 37,000, glass transition temperature: 19°C) and a plasticizer (dibutyl phthalate) were added to the nylon mill. Here, 28.4 parts by mass of binder and 3.2 parts by mass of plasticizer were added in terms of solid content. Next, a slurry was prepared by further milling for 20 hours.

[0059] The prepared slurry was then transferred to a jacketed, round-bottomed, cylindrical vacuum degassing vessel equipped with an anchor-shaped stirrer. The slurry was then concentrated and degassed under reduced pressure at a jacket temperature of 40°C while the stirrer was rotating at 200 rpm. This resulted in a slurry with a viscosity of 3 Pa·s at 25°C.

[0060] Next, using a coating device, the slurry was continuously coated onto a PET film substrate film. The slurry was coated using a doctor blade method. The coated slurry was then dried at 100°C for 2 hours in the same coating device. This resulted in a sheet approximately 0.32 mm thick and long in plan view. After peeling this sheet from the substrate film, three green sheets (30 cm square) each having a rectangular shape in plan view were obtained using a Thomson blade. Hereinafter, the surface of the green sheet that was in contact with the PET film substrate film will be referred to as the "PET surface." Furthermore, the surface of the green sheet opposite the PET surface in the thickness direction of the sheet will sometimes be referred to as the "air surface."

[0061] (Setter) First, a mixed powder identical to the raw material powder used in producing the green sheet was prepared. The mixed powder was then placed in a nylon mill loaded with zirconia balls. A mixed powder was obtained by dry mixing for 20 hours. The mixed powder was then placed in an alumina sagger, which was then placed in a high-temperature box-type electric furnace. The electric furnace was then heated to 1350°C and maintained there for 2 hours. This resulted in calcining the mixed powder in the sagger. The calcined mixed powder was then pulverized in a mortar and mortar, and then sieved through a wire mesh with 500 μm openings. The powder that passed through the wire mesh was then collected.

[0062] Next, the powder sieved through a wire mesh was placed on the mounting surface of an alumina setter (manufactured by Yotai Co., Ltd., alumina approximately 99%, porosity: 16.9%, bulk specific gravity 3.2). At this time, the powder was spread thinly and uniformly on the mounting surface using a brush. Next, the setter with the powder spread on it was placed in a high-temperature box-type electric furnace, which was heated to 1350°C and held for 2 hours. This caused a mixed powder identical to the raw material powder to be baked onto the mounting surface of the setter. After the setter was cooled, the entire amount of the powder was baked in. In other words, no falling off of the powder was observed after the setter was cooled.

[0063] (Lithium conductive sheet) First, for the air side of each green sheet, the composition is Li 3X La 2 / 3-X LLTO powder (particle size: 20-50 μm) of TiO3 (X=0.3) was supplied. At this time, the powder amount was 5 mg / cm 2 Using a fiber material, LLTO powder was uniformly attached to the air side so that the green sheet was uniformly adhered to the air side. Next, one green sheet was placed on the mounting surface of an alumina setter (manufactured by Yotai Co., Ltd., alumina approximately 99%, porosity: 16.9%, bulk specific gravity: 3.2). At this time, one green sheet was placed on the setter so that the PET side was in contact with the mounting surface. Next, two other green sheets (with powder already applied) were stacked in order on the green sheet on the setter to form a laminate.

[0064] Next, the setter and laminate were placed in an electric furnace, and each green sheet was degreased by heating the electric furnace from room temperature to 500°C over 10 hours. Next, the setter and the laminate including the degreased green sheets were placed in a high-temperature box-type electric furnace, and the electric furnace was heated to 1350°C and held at that temperature for 1 hour, thereby firing each green sheet. This resulted in three perovskite-based composite oxide sheets (lithium conductive sheets) composed of lanthanum, lithium, and titanium oxides. Each sheet was approximately 20 cm square in plan view. The thickness of each sheet was approximately 0.5 mm (approximately 500 μm).

[0065] <Example 2> Three 5 cm square lithium conductive sheets were obtained by carrying out the same procedure as in Example 1 above, except that the size of the green sheet punched out with the Thomson blade was 7.5 cm square.

[0066] <Comparative Example 1> A single green sheet was placed on a setter, and then degreased and fired without forming a laminate, by carrying out the same procedure as in Example 1 above, to obtain a single 20 cm square lithium conductive sheet.

[0067] <Comparative Example 2> A single green sheet was placed on a setter, and then degreased and fired without forming a laminate, in the same manner as in Example 2 above, to obtain a single 5 cm square lithium conductive sheet.

[0068] [Evaluation method] The Li ion conductivity of the lithium conductive sheet of Example 1 was evaluated by the following method. The distortion rates of the lithium conductive sheets of Example 1 and Comparative Example 1 were evaluated by the following method. The composition difference between the lithium conductive sheets of Example 2 and Comparative Example 2 was evaluated by the following method.

[0069] (Li-ion conductivity) One lithium conductive sheet produced in Example 1 and two pieces of filter paper cut to a size of 10 mm x 10 mm were prepared. Note that the prepared lithium conductive sheet was not surface-polished. Next, two pieces of filter paper were impregnated with a 1 M lithium chloride aqueous solution, and the lithium conductive sheet was sandwiched between the two pieces of filter paper. Next, a stainless steel mesh (1 cm x 5 cm) functioning as a positive electrode or a negative electrode was contacted with the exposed surface of one filter paper and the exposed surface of the other filter paper, respectively. Next, using a small vice, the lithium conductive sheet and other components were fixed in the following configuration: vice - stainless steel mesh - filter paper - lithium conductive sheet - filter paper - stainless steel mesh - vice. Next, a Cole-Cole plot was measured using an impedance analyzer (Toyo Corporation, "SI 1260") at a measurement frequency of 10 Hz to 30 MHz and a measurement temperature of 27°C. The lithium ion conductivity of the lithium conductive sheet as a whole was calculated from the measurement data.

[0070] The lithium ion conductivity I (S / cm) of the lithium conductive sheet is calculated by the sum of the resistance values ​​R (Ω) between the particles and the particles obtained by the Cole-Cole plot, and the electrode area EA (cm) when the filter paper in contact with the sheet is considered as an electrode. 2 ) and the thickness T (cm) of the lithium conductive sheet, it can be expressed by the following formula: I=1 / R× T / EA

[0071] Here, the main surface of the lithium conductive sheet (400 cm 2 ) 50 locations were randomly selected without overlapping and the lithium ion conductivity was measured at each location. The average value of the lithium ion conductivity measurement results obtained at the 50 locations was 4.9 × 10 -4 (S / cm), and the standard deviation of the measurement results is 6.8 × 10 -5 (S / cm).

[0072] (Distortion rate) First, each of the lithium conductive sheets of Example 2 and Comparative Example 2 was placed on a horizontal table of a laser displacement meter (manufactured by Keyence Corporation, "LK-G35"). Next, the position of the lithium conductive sheet in the Z-axis direction was measured using the laser displacement meter. The Z-axis position was obtained at 5 mm intervals. As a result, when a value (6T) six times the thickness T of the lithium conductive sheet was set as a threshold, portions where the position in the Z-axis direction exceeded this threshold were identified. Next, the area A of the main surface of the lithium conductive sheet facing the horizontal table was measured. all (cm 2 ) of the area corresponding to the above part, A deviation (cm 2 ) was calculated. And the area A deviation Area A allThe strain rate (%) of the lithium conductive sheet was calculated by dividing by the strain rate. The strain rates of Example 1 and Comparative Example 1 are shown in Table 1. In Table 1, the strain rate of the lithium conductive sheet located on the upper side of the laminate after firing is designated "Example 1 (Top)," the strain rate of the lithium conductive sheet located on the lower side (setter side) of the laminate after firing is designated "Example 1 (Bottom)," and the strain rate of the lithium conductive sheet located at the center of the laminate after firing is designated "Example 1 (Middle)." As shown in Table 1, all of the strain rates of Example 1 are significantly smaller than that of Comparative Example 1. In addition, the strain rate tends to be smaller as the lithium conductive sheet is located at the upper side of the laminate. Three lithium conductive sheets were produced twice separately under the same conditions as Example 2. The strain rates of the upper lithium conductive sheets were all 0, the strain rates of the central lithium conductive sheets were at most 0.9, and the strain rate of the lower lithium conductive sheets was at most less than 7. Furthermore, when one lithium conductive sheet was produced twice under the same conditions as in Comparative Example 2, the strain rate of the lithium conductive sheet exceeded 15 in both cases.

[0073] [Table 1]

[0074] (composition analysis) For each of Example 2 and Comparative Example 2, composition analysis was performed using ICP analysis (inductively coupled plasma analysis). First, 0.05 g of a sample obtained by crushing a portion of each lithium conductive sheet in a mortar was placed in a mixed solution of 15 mL of sulfuric acid and 5 g of ammonium sulfate. Next, the mixed solution was heated with a microwave to dissolve the sample, and the solution was diluted to 100 mL to prepare a test solution for ICP analysis. The composition of the lithium conductive sheet was then analyzed from the test solution using an ICP-OES (Thermo Fisher Scientific, "iCAP6500 Duo"). Quantitation was performed using a matrix matching method. For each of Example 2 and Comparative Example 2, the composition of the lithium conductive sheet was analyzed using four different test solutions. The samples contained in each test solution were formed from different parts of the lithium conductive sheet.

[0075] Here, the molar ratio of lithium to lanthanum in the raw material powder is MR before The molar ratio of lithium to lanthanum in the lithium conductive sheet is MR after The latter (MR after ) is the average value of the lithium to lanthanum molar ratio obtained from each test solution. The percentage of the absolute value of the difference in the above molar ratios (|MR after -MR before |×100) is considered to be the composition difference between each lithium conductive sheet and the raw material powder in the slurry. The larger the composition difference, the greater the degree of Li scattering during the production of the lithium conductive sheet. The composition differences between Example 2 and Comparative Example 2 are shown in Table 2. As shown in Table 2, the composition difference in Example 2 is significantly smaller than the composition difference in Comparative Example 2.

[0076] [Table 2] [Explanation of symbols]

[0077] 1...lithium conductive sheet, 1a, 10a...first main surface, 1b, 10b...second main surface, 10...green sheet, 20...powder, 50...setter, 50a...mounting surface, S...laminated body.

Claims

1. The composition is Li ３Ｘ La ２／３－Ｘ TiO ３ (X is 0.05 or more and 0.3 or less), The area of ​​the main surface is 30 cm ２ That's all, The thickness is 10 μm or more and 1000 μm or less, The distortion rate when viewed from the extending direction of the main surface is 10% or less, The average value of the lithium ion conductivity measurement results of 50 randomly selected points was 3.0 × 10 －４ S / cm or more, and the standard deviation of the measurement results is 1.0 × 10 －４ S / cm or less, The distortion rate is a value obtained by dividing the area of ​​a portion of the main surface, when placed on a horizontal surface, that is at least six times the thickness away from the horizontal surface by the area of ​​the main surface, No surface polishing has been done. Lithium conductive sheet.

2. The lithium conductive sheet according to claim 1 , wherein X is 0.1 or more and 0.3 or less.

3. The lithium conductive sheet according to claim 1 or 2, wherein the distortion rate is 7% or less.

4. a first step of forming a green sheet by drying a coating of a slurry containing oxides containing lanthanum, titanium, and lithium; a second step of preparing a plurality of the green sheets and then supplying powder having an average particle size of 0.1 μm or more and 700 μm or less onto each main surface of the plurality of the green sheets; a third step of forming a laminate by stacking a plurality of the green sheets after the second step; a fourth step of degreasing the laminate and then firing the laminate; Equipped with The powder contains 80 mass% or more of an oxide powder containing lanthanum, titanium, and lithium, In the third step and the fourth step, the laminate is not pressurized. A method for producing a lithium conductive sheet.

5. The lithium conductive sheet has a composition of Li 3X La 2 / 3-X TiO 3 (X is 0.05 or more and 0.3 or less), the area of ​​the main surface of the lithium conductive sheet is 30 cm 2 or more; The lithium conductive sheet has a thickness of 10 μm or more and 1000 μm or less, The method for producing a lithium conductive sheet according to claim 4 , wherein the surface is not polished after the fourth step.

6. 6. The method for producing a lithium conductive sheet according to claim 4 or 5, wherein the first step uses the slurry produced by wet mixing a lanthanum raw material, a titanium raw material, a lithium raw material, a binder, and a solvent.

7. 6. The method for producing a lithium conductive sheet according to claim 4, wherein the first step uses the slurry produced by wet mixing an oxide raw material containing lanthanum, titanium, and lithium, a binder, and a solvent.

8. In the fourth step, the laminate placed on the mounting surface of a setter is fired, at least a portion of the mounting surface has an oxide containing at least one of lanthanum, titanium, and lithium; The method for producing a lithium conductive sheet according to any one of claims 4 to 7, wherein the oxide is formed by baking a powder containing at least one of a lanthanum raw material, a titanium raw material, and a lithium raw material onto the placement surface.

9. In the second step, the amount of the powder to be supplied is 0.01 mg / cm ２ 10mg / cm or more ２ The method for producing a lithium conductive sheet according to any one of claims 4 to 8, wherein:

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