Coating solution manufacturing method and coating formation method

Abstract

The present invention involves preparing (S1) a stock solution containing a metal alkoxide, and then adding (S2, S3) water molecules to the prepared stock solution. As a result, in a mixed solution containing the stock solution and water molecules, gelling is initiated through a hydrolysis / dehydration condensation reaction of the metal alkoxide. At that moment, even if a high molecular weight gel having a large molecule size is generated, such a gel having a large molecule size is removed from the mixed solution when the solution is filtered in a subsequent filtration step (S4).

Description

[Technical Field]

[0001] The present invention relates to a coating solution that is the source of a fine particle coating formed on the surface of powder. [Background technology]

[0002] For example, surface modification and composite technology is used for the positive electrode active material powder of all-solid-state batteries. In surface modification and composite technology, the surface of the powder particles is coated with fine particles, forming a fine particle coating that gives the particle surface functionality.

[0003] The coating solution that forms the film on the particles is prepared by the sol-gel method, which utilizes the hydrolysis and dehydration condensation reaction of metal alkoxides. A gel film is then formed on the surface of the particles from the coating solution, which is then dried to form a dry gel film, which is then baked to obtain particles whose surfaces are covered with a film of fine particles. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-165467 Summary of the Invention [Problem to be solved by the invention]

[0005] The hydrolysis and dehydration condensation reaction of metal alkoxides occurs when water molecules are added to metal alkoxides. Therefore, before the coating solution forms a gel coating on the particle surface, gelation can begin, resulting in the formation of large molecular gels. These large molecular gels cause segregation in the coating. The higher the demand for thinner coatings, the greater the degree of segregation caused by large molecular gels, making the coating more likely to be uneven and have varying thicknesses.

[0006] An object of the present invention is to provide a method for producing a coating solution capable of forming a coating with little segregation, and a method for forming a coating using the coating solution. [Means for solving the problem]

[0007] In order to achieve the above-mentioned object, a coating solution manufacturing method according to one aspect of the present invention is a method for manufacturing a coating solution that serves as the basis for the coating of fine particles formed on the surfaces of particles by a sol-gel method utilizing the hydrolysis and dehydration condensation reaction of a metal alkoxide, and includes a stock solution manufacturing step of manufacturing a stock solution containing a metal alkoxide, a hydration step of adding water molecules to the stock solution manufactured in the stock solution manufacturing step, and a filtration step of filtering the solution obtained by adding water molecules to the stock solution in the hydration step.

[0008] According to this method, a stock solution containing metal alkoxide is prepared, and then water molecules are added to the prepared stock solution. This initiates gelation through the hydrolysis and dehydration condensation reaction of the metal alkoxide. Even if large molecular gels are produced during this process, the solution is subsequently filtered, removing the large molecular gels. Therefore, by supplying the filtered solution to the particles as a coating solution, a coating with minimal segregation can be formed on the particle surface.

[0009] The coating solution manufacturing method may further include, before the filtering step, an additive adding step of adding an additive containing a ligand to the stock solution prepared in the stock solution preparing step.

[0010] By adding an additive containing a ligand to the stock solution, the ligand binds to the metal contained in the stock solution, suppressing cross-linking of the metal alkoxide, and as a result, preventing the formation of large-molecule gel in the solution containing the stock solution and water molecules.

[0011] A coating solution manufacturing method according to another aspect of the present invention is a method for manufacturing a coating solution that serves as the basis for the coating of fine particles formed on the surfaces of particles by a sol-gel method utilizing the hydrolysis and dehydration condensation reaction of metal alkoxide, and includes a stock solution manufacturing step of manufacturing a stock solution containing a metal alkoxide, an additive adding step of adding an additive containing a ligand to the stock solution manufactured in the stock solution manufacturing step, and a hydration step of adding water molecules to the stock solution manufactured in the stock solution manufacturing step.

[0012] According to this method, a stock solution containing a metal alkoxide is prepared, and then an additive containing a ligand is added to the prepared stock solution. Water molecules are then added to the stock solution. When water molecules are added to the stock solution, gelation begins due to the hydrolysis and dehydration condensation reaction of the metal alkoxide. At this time, because the solution contains an additive containing a ligand, the ligand binds to the metal in the solution, suppressing cross-linking of the metal alkoxide. As a result, a solution in which the formation of large molecular gels is suppressed is supplied to the particles as a coating solution, allowing for the formation of a coating with minimal segregation on the particle surface.

[0013] A coating solution manufacturing method according to yet another aspect of the present invention is a method for manufacturing a coating solution that serves as the basis for the coating of fine particles formed on the surfaces of particles by a sol-gel method utilizing the hydrolysis and dehydration condensation reaction of a metal alkoxide, and includes a stock solution preparation step of preparing a stock solution containing a metal alkoxide, and an additive application step of adding an additive containing a ligand to the stock solution prepared in the stock solution preparation step, and the solution obtained by adding the additive to the stock solution in the additive application step is used as the coating solution without adding water molecules to the solution.

[0014] According to this method, a stock solution containing a metal alkoxide is prepared, and then an additive containing a ligand is added to the prepared stock solution. The solution containing the stock solution and additive is then supplied to the particles as a coating solution without adding water molecules. Therefore, after the coating solution is supplied to the particles, gelation occurs due to the hydrolysis and dehydration condensation reaction of the metal alkoxide in the coating solution. As a result, the formation of large molecular gels in the coating solution before it is supplied to the particles is suppressed, allowing for the formation of coatings with minimal segregation on the particle surfaces.

[0015] The additive may be, for example, ethyl acetoacetate.

[0016] A coating solution manufacturing method according to yet another aspect of the present invention is a method for manufacturing a coating solution that serves as the basis for the coating of fine particles formed on the surfaces of particles by a sol-gel method utilizing the hydrolysis and dehydration condensation reaction of metal alkoxide, and includes a stock solution manufacturing step of manufacturing a stock solution containing metal alkoxide, and a filtration step of filtering the stock solution manufactured in the stock solution manufacturing step, and the stock solution is converted into the coating solution without adding water molecules to the stock solution after filtration in the filtration step.

[0017] According to this method, a stock solution containing metal alkoxide is prepared and then filtered. When the stock solution comes into contact with the atmosphere, water molecules from the atmosphere enter the stock solution, initiating gelation through the hydrolysis and dehydration condensation reaction of the metal alkoxide. Even if large gels are formed during this process, the stock solution is filtered, removing the large gels from the stock solution. The stock solution is then supplied to the particles as a coating solution without actively adding water molecules. Therefore, after the coating solution is supplied to the particles, gelation through the hydrolysis and dehydration condensation reaction of the metal alkoxide in the coating solution begins. As a result, the formation of large gels in the coating solution before it is supplied to the particles is suppressed, allowing for the formation of coatings with minimal segregation on the particle surfaces.

[0018] In the hydration step, water molecules may be actively added to the raw solution, or the raw solution may absorb moisture from the atmosphere, thereby adding water molecules to the raw solution.

[0019] The hydration step may be carried out in an atmosphere maintained at a predetermined low temperature.

[0020] In the hydration process under a low-temperature atmosphere, the atmosphere surrounding the raw solution is kept at a low temperature, which reduces the vapor pressure of the solvent in the raw solution and delays the hydrolysis and dehydration condensation reactions, resulting in a more homogeneous sol solution.

[0021] The coating solution manufacturing method may further include a cooling step of cooling the stock solution prepared in the stock solution preparation step.

[0022] By cooling the raw solution to a low temperature, the evaporation of the solvent from the raw solution can be suppressed, resulting in a more homogeneous sol solution.

[0023] The cooling step may be continued until the end of the water addition step.

[0024] By keeping the raw solution at a low temperature until the end of the water addition process, the evaporation of the solvent in the raw solution can be suppressed and the hydrolysis and dehydration condensation reaction can be delayed, resulting in a more homogeneous sol solution.

[0025] A coating formation method according to another aspect of the present invention is a method for forming a coating of fine particles on the surfaces of powder particles, and includes a coating solution preparation step of preparing a coating solution that serves as the basis for the coating; a dispersion step of introducing a slurry of a mixture of powder and coating solution into a flow path and dispersing the slurry flowing through the flow path into individual particles using a high-speed fluid airflow; a drying step of transporting the powder dispersed into individual particles in the dispersion step by using the airflow and drying the coating solution during transport; and a collection step of collecting the powder coated with the coating solution dried in the drying step, wherein the coating solution preparation step uses the coating solution production method described above.

[0026] This method can achieve the effect described in relation to each of the coating solution manufacturing methods, that is, the effect of forming a coating with little segregation on the surface of powder particles. [Effects of the Invention]

[0027] According to the present invention, it is possible to prevent a coating solution containing a gel with a large molecular size from being supplied to particles, and therefore it is possible to form a coating with little segregation on the surface of the particles. [Brief explanation of the drawings]

[0028] [Figure 1] 1 is a cross-sectional view illustrating the configuration of a coating apparatus in which a coating formation method according to one embodiment of the present invention is carried out. [Figure 2] FIG. 1 is a process diagram showing the flow of a coating solution preparation method (manufacturing method). [Figure 3] FIG. 1 is a process diagram showing the flow of another method for preparing (producing) a coating solution. [Figure 4] FIG. 10 is a process diagram showing the flow of yet another method for preparing (producing) a coating solution. [Figure 5] FIG. 4 is a process diagram showing the flow of a preparation method in which the filtration step is omitted from the preparation method shown in FIG. 3. [Figure 6] FIG. 4 is a process diagram showing the flow of a preparation method in which the water-added solution preparation step is omitted from the preparation method shown in FIG. 3. [Figure 7] FIG. 7 is a process diagram showing the flow of a preparation method in which the hydration step of the preparation method shown in FIG. 6 is changed to a hydration step under a low-temperature atmosphere. [Figure 8] FIG. 3 is a process diagram showing the flow of a preparation method in which the water-added solution preparation step is omitted from the preparation method shown in FIG. 2. [Figure 9] FIG. 7 is a process diagram showing the flow of a preparation method in which the filtration step is omitted from the preparation method shown in FIG. 6. [Figure 10] FIG. 4 is a process diagram showing the flow of a preparation method in which the water-added solution preparation step, water addition step, and filtration step are omitted from the preparation method shown in FIG. [Figure 11]FIG. 3 is a process diagram showing the flow of a preparation method in which the water-added solution preparation step and the water addition step are omitted from the preparation method shown in FIG. 2. DETAILED DESCRIPTION OF THE INVENTION

[0029] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0030] <Coating equipment> FIG. 1 is a cross-sectional view illustrating the configuration of a coating apparatus 1 for carrying out a coating film forming method according to one embodiment of the present invention.

[0031] The coating apparatus 1 is an apparatus for a coating process (film formation process) in which fine particles are bonded to powder particles to produce a composite powder in which a film of fine particles is formed on the surface of each particle. The coating apparatus 1 is equipped with a raw material tank 2, a dispersion section 3, a drying section 4, and a collection section 5.

[0032] The raw material tank 2 stores a slurry that is a mixture of powder and a coating solution that is the source of the coating. The raw material tank 2 that stores the slurry is sealed, and the inside of the raw material tank 2 is isolated from the outside air. The slurry is prepared, for example, in a glove box that is isolated from the outside air, and the powder and the coating solution are weighed and mixed at a weight ratio set so that the coating on the surface of the particles has a predetermined thickness. The slurry stored in the raw material tank 2 is stirred using a stirring mechanism 21 such as a magnetic stirrer. The slurry is sucked out of the raw material tank 2 by the action of the liquid feed pump 22, and the sucked slurry is supplied to the dispersion section 3.

[0033] The dispersion section 3 includes a slurry passage 31, a first dry air passage 32, a second dry air passage 33, and a third dry air passage .

[0034] The slurry flow channel 31 extends linearly in the vertical direction. The slurry sucked out from the raw material tank 2 is supplied to the upper end of the slurry flow channel 31. The slurry supplied to the slurry flow channel 31 flows through the slurry flow channel 31 and is discharged downward from the lower end of the slurry flow channel 31.

[0035] Instrument air from which moisture has been removed by a dry air unit 35 is supplied to the first dry air flow path 32, the second dry air flow path 33, and the third dry air flow path 34. The instrument air is air (atmospheric air) pressurized to a predetermined pressure. That is, high-pressure dry air is supplied to the first dry air flow path 32, the second dry air flow path 33, and the third dry air flow path 34. Note that, in addition to atmospheric air, various gases such as nitrogen, carbon dioxide, and inert gases can be used as dry air.

[0036] The first dry air flow path 32 extends linearly in the vertical direction, and its lower end is open at a position higher than the lower end of the slurry flow path 31. By discharging the dry air from the first dry air flow path 32 in the same direction as the slurry flow path 31, the influence of the collision pressure of the dry air from the second dry air flow path 33 is suppressed, and the flow of the slurry is regulated.

[0037] The second dry air flow paths 33 are provided separately on one side of a vertical line and on the other side, each extending at an angle of 45° relative to the up-down direction (vertical direction) toward a collision position P set below the slurry flow path 31. The end of each second dry air flow path 33 on the collision position P side is open. While the dry air flows through each second dry air flow path 33, the flow velocity of the dry air increases significantly, and for example, the flow velocity reaches the sonic velocity or higher. A dry air stream having a flow velocity exceeding the sonic velocity is ejected from the open end of each second dry air flow path 33, and these air streams collide at the collision position P. As the slurry discharged from the lower end of the slurry flow path 31 passes through the collision position P, it is subjected to a shear force from the air stream colliding at the collision position P, and is dispersed into powder having the coating solution adhered to its surface.

[0038] The third dry air flow paths 34 are provided separately on one side and the other side of a vertical line, and each extends horizontally relative to the slurry flow path 31. The end of each third dry air flow path 34 is open below the lower end of the slurry flow path 31 and above the collision position P of the second dry air flow path 33. The dry air from the third dry air flow path 34 is discharged in a direction horizontal to the slurry flow path 31, thereby suppressing the spreading of the slurry at the lower end of the slurry flow path 31 and regulating the flow of the slurry, and suppressing adhesion to the inside of the dispersion section 3.

[0039] The drying section 4 integrally includes a cylindrical section 41 having a cylindrical peripheral surface and a conical section 42 that is continuous with the cylindrical section 41 and has a generally conical shape that narrows with increasing distance from the cylindrical section 41. The drying section 4 is disposed directly below the dispersion section 3 such that the center line of the cylindrical section 41 extends in the vertical direction.

[0040] An assist air inlet 43 is formed on the circumferential surface of the cylindrical portion 41. Air sucked through an intake filter 44 is supplied to the assist air inlet 43 as assist air through an assist air supply pipe 45. Air is sucked in by a dry blower 46, and the assist air used for drying is exhausted together with other dry air from the discharge side of the dry blower 46. A heat exchanger 47 that exchanges heat between the assist air and the exhaust of the dry blower 46 and a dry heater 48 that heats the air are disposed midway along the assist air supply pipe 45. As a result, heated dry air is introduced into the cylindrical portion 41 from the assist air inlet 43 as assist air. Note that various gases, such as nitrogen, carbon dioxide, and inert gases, can be used as assist air in addition to air.

[0041] The assist air inlet 43 and the assist air supply pipe 45 are formed so that assist air is blown out from the assist air inlet 43 in a tangential direction to the inner circumferential surface of the cylindrical portion 41. Therefore, the assist air introduced into the cylindrical portion 41 from the assist air inlet 43 becomes a vortex airflow that flows along the inner circumferential surface of the cylindrical portion 41 and flows from the cylindrical portion 41 into the conical portion 42.

[0042] Powder dispersed into particles is introduced into the cylindrical section 41 from the dispersion section 3 above. The powder introduced into the cylindrical section 41 is then carried by the assist air current formed within the cylindrical section 41 through the drying section 4 toward the conical section 42. During this transport, the coating solution adhering to the surface of each particle dries, producing a powder in which the surface of each particle is coated with the dried coating solution (coating precursor) (hereinafter, this powder will be referred to as "dry gel powder"). Furthermore, droplets of the coating solution that do not contain powder particles dry, producing dried pieces of the coating solution.

[0043] To accelerate drying of the coating solution in the drying section 4, the drying section 4 may be heated by a heater. For the same reason, the dry air supplied to the first dry air flow path 32, the second dry air flow path 33, and the third dry air flow path 34 of the dispersion section 3 may be heated by a heater.

[0044] The collection unit 5 includes a collection cyclone 51 and a collection filter 52 .

[0045] One end of an intake pipe 53 is connected to the collecting cyclone 51. The other end of the intake pipe 53 is connected to the suction port of the drying blower 46, which serves as a suction source. As a result, when the drying blower 46 is activated, air within the collecting cyclone 51 is sucked into the intake pipe 53, creating a negative pressure within the collecting cyclone 51. The collecting cyclone 51 is also provided with a powder introduction section 54. A sanitary pipe 55 extending from the lower end of the conical section 42 of the drying section 4 is connected to the powder introduction section 54. The dry gel powder and dried pieces of the coating solution that reach the lower end of the conical section 42 of the drying section 4 flow through the sanitary pipe 55 due to the negative pressure within the collecting cyclone 51 and are sucked into the collecting cyclone 51. The airflow containing the dry gel powder and dried pieces of the coating solution swirls in the collecting cyclone 51, and the resulting centrifugal force and gravity separate the dry gel powder, which has a relatively large particle size and mass, from the dried pieces of the coating solution, which has a relatively small particle size and mass. The dry gel powder is stored in a collecting box 56 connected to the bottom of the collecting cyclone 51.

[0046] The collection filter 52 is installed midway through the intake pipe 53. The dried pieces of the coating solution separated in the collection cyclone 51 are carried by air and sucked into the intake pipe 53, where they are captured by the collection filter 52. Therefore, the collection filter 52 allows only air to pass through.

[0047] When the coating apparatus 1 is used to produce a positive electrode active material powder for an all-solid-state battery, the powder mixed with the coating solution in the raw material tank 2 is, for example, a lithium metal composite oxide, and is made up of particles with an average particle size of about 2 to 30 μm. Metal elements constituting the powder include Co, Ni, Mn, Ti, Fe, Al, etc., but other elements may also be contained to improve the electrochemical properties. Specifically, particles constituting the powder include LiCoO2, LiNiO2, LiMn2O4, LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2, Li4Ti5O 12 , LiFePO4, LiNi 0.8 Co 0.15 Al 0.05 Examples of particles include O2. The coating solution is described next.

[0048] <How to prepare the coating solution> FIG. 2 is a process diagram showing the flow of a coating solution preparation method (manufacturing method).

[0049] The coating solution is prepared in a glove box. The atmosphere in the glove box is controlled by filling it with a nitrogen atmosphere or dry air with a low dew point (for example, -30°C or less). Tools such as raw material containers, containers for preparing the solution, and electronic balances are placed in the glove box before preparation begins, and moisture is removed (dried). The atmosphere in the glove box may also be controlled using an inert gas other than nitrogen.

[0050] Hereinafter, a coating solution used to produce a positive electrode active material powder for an all-solid-state battery will be taken as an example.

[0051] Equimolar amounts of ethoxylithium (LiOC2H5) and pentaethoxyniobium (Nb(OC2H5)5) are weighed in a glove box. These equimolar amounts are then dissolved in ultra-dehydrated ethanol to a concentration of 0.4 mol / L, producing a lithium-niobium mixed ethoxy solution (stock solution preparation step: S1).

[0052] The lithium-niobium mixed ethoxylate solution is placed in a raw material container, which is then sealed and stored in a desiccator. The solution is then divided into small portions as needed and used to prepare the coating solution. Alternatively, the lithium-niobium mixed ethoxylate solution may be used in the next step without being stored.

[0053] If the lithium-niobium ethoxylate solution is stored in a source container, the source container is opened in an atmosphere-controlled glove box and the required amount of lithium-niobium ethoxylate solution is weighed out to prepare the coating solution.

[0054] In the step following the stock solution preparation step, a water-added solution is prepared, also in the glove box (water-added solution preparation step: S2). That is, in the atmosphere-controlled glove box, pure water in a molar amount corresponding to 0.5 to 3 moles per mole of pentaethoxyniobium is added to super-dehydrated ethanol, and they are thoroughly stirred to dissolve, thereby producing (preparing) water-added ethanol as a water-added solution. The stock solution preparation step (S1) and the water-added solution preparation step (S2) may be performed in parallel, or may be performed in reverse order.

[0055] Pure water is generally used as a catalyst, but depending on the film formation conditions (coating conditions), an acid catalyst such as an organic acid with a low boiling point or a base catalyst may be added to control the dehydration condensation reaction. Also, depending on the film formation conditions, it is possible to use only ultra-dehydrated ethanol without adding water and / or an acid catalyst.

[0056] Then, in an atmosphere-controlled glove box, aqueous ethanol is slowly added to the lithium-niobium ethoxylate mixed solution to prepare a mixed solution (sol-gel solution) diluted to the target molar concentration (0.1-0.3 mol / L) (water addition step: S3).

[0057] The lithium-niobium mixed ethoxylate solution and the aqueous ethanol are mixed by adding the aqueous ethanol dropwise to the lithium-niobium mixed ethoxylate solution while stirring it with a stirring bar and magnetic stirrer. However, any method can be used as long as it can uniformly mix the lithium-niobium mixed ethoxylate solution and the aqueous ethanol.

[0058] In a mixed solution of lithium-niobium ethoxylate and water-added ethanol, the hydrolysis and dehydration condensation of metal alkoxides occur almost simultaneously due to the action of added water molecules, forming an inorganic polymer in which lithium and niobium are uniformly mixed. At this time, a gel with relatively large molecular size is formed due to the highly active water molecule clusters at the beginning of the reaction.

[0059] Therefore, in the next step, the mixed solution is filtered through a filter with a pore size of 0.1 to 1 μm to remove the polymer gel with a large molecular size (filtration step: S4). As the filter, a membrane filter made of a hydrophobic material that is compatible with organic solvents is mainly used, but depending on the conditions, a prefilter, a cross-flow filter, etc. may also be used in combination.

[0060] The mixed solution from which the polymer gel with a large molecular size has been removed is suitably used as a coating solution for coating treatment in the coating device 1.

[0061] <Action and effect> As described above, after a stock solution containing a metal alkoxide is prepared, water molecules are added to the prepared stock solution. This causes gelation to occur in the mixed solution containing the stock solution and water molecules due to the hydrolysis and dehydration condensation reaction of the metal alkoxide. Even if a large molecular size polymer gel is produced during this process, it is removed from the solution by filtering the mixed solution in the subsequent filtration step (S4). This prevents the mixed solution containing the large molecular size polymer gel from being supplied to the powder particles as a coating solution, allowing for the formation of a coating with minimal segregation on the particle surface.

[0062] <Other methods for preparing coating solution> FIG. 3 is a process diagram showing the flow of another method for preparing (producing) a coating solution.

[0063] In the preparation method shown in Figure 3, a stock solution preparation step (S11) in which a lithium-niobium mixed ethoxylate solution is prepared as a stock solution is followed by an additive application step (S12). Furthermore, after a water-added solution preparation step (S13) is performed, a water addition step (S14) and a filtration step (S15) are performed in this order. The stock solution preparation step (S11), the additive application step (S12), and the water-added solution preparation step (S13) may be performed in parallel or in reverse order.

[0064] The stock solution preparation step (S11), the water-added solution preparation step (S13), the water-adding step (S14), and the filtration step (S15) are the same as the stock solution preparation step (S1), the water-added solution preparation step (S2), the water-adding step (S3), and the filtration step (S4) shown in FIG. 2, respectively, and therefore detailed explanations of the stock solution preparation step (S11), the water-added solution preparation step (S13), the water-adding step (S14), and the filtration step (S15) will be omitted here.

[0065] In the stock solution preparation step (S11), the raw material container is opened in an atmosphere-controlled glove box, and a predetermined amount of lithium-niobium mixed ethoxy solution required for preparing the coating solution is weighed out. Then, in the additive addition step (S12), ethyl acetoacetate is added as an additive to the weighed lithium-niobium mixed ethoxy solution in a molar amount corresponding to 0.5 to 2.5 moles per mole of pentaethoxyniobium in the lithium-niobium mixed ethoxy solution.

[0066] In the water addition step (S14), the water-added ethanol prepared in the water-added solution preparation step (S13) is added to the lithium-niobium mixed ethoxy solution to which the additive has been added.

[0067] <Action and effect> By adding ethyl acetoacetate, an additive containing a ligand, to the lithium-niobium mixed ethoxylate solution, the ligand chelates with the metal contained in the solution, suppressing cross-linking of the metal alkoxide. This prevents the formation of large molecular polymer gels in the solution and in the solution containing water molecules. As a result, a coating with minimal segregation can be formed on the surface of the powder particles.

[0068] Although ethyl acetoacetate is preferred as the additive, other additives are possible, such as β-diketones such as acetylacetone that chelate to metal alkoxides such as pentaethoxyniobium, β-keto acids such as acetoacetic acid and their ester compounds, dicarboxylic acids such as malonic acid and their ester compounds, carboxylic acid anhydrides such as propionic anhydride, or β-dicarbonyl compounds, as long as they have a boiling point of 200°C or less and are highly soluble in an ethanol solution.

[0069] <Another method for preparing the coating solution> FIG. 4 is a process diagram showing the flow of yet another method for preparing (producing) a coating solution.

[0070] In the preparation method shown in Figure 4, after the stock solution preparation step (S21) in which a lithium-niobium mixed ethoxylate solution is prepared as a stock solution, the additive application step (S22) and the water-added solution preparation step (S23) are performed in this order. Then, the solution cooling step (S24) is performed. Then, after the solution cooling step (S24), the water addition step (S25) and the filtration step (S26) are performed in this order. Note that the stock solution preparation step (S21), the additive application step (S22), and the water-added solution preparation step (S23) may be performed in parallel or in reverse order.

[0071] The stock solution preparation step (S21), water-added solution preparation step (S23), water addition step (S25), and filtration step (S26) are the same as the stock solution preparation step (S1), water-added solution preparation step (S2), water addition step (S3), and filtration step (S4), respectively, shown in Figure 2. The additive application step (S22) is the same as the additive application step (S12) shown in Figure 3. Detailed explanations of the stock solution preparation step (S21), additive application step (S22), water-added solution preparation step (S23), water addition step (S25), and filtration step (S26) will be omitted here.

[0072] In an atmosphere-controlled glove box, an additive-added stock solution, for example, a solution in which ethyl acetoacetate is added to a lithium-niobium mixed ethoxylate solution, is prepared in an additive-adding step (S22). Also, in the same glove box, a water-added solution, for example, water-added ethanol, is prepared in a water-added solution preparation step (S23).

[0073] In the solution cooling step (S24), the prepared additive-added stock solution and water-added solution are each cooled to a low temperature (for example, 10°C or lower). The cooling of each solution is carried out, for example, using a cooling agent, and continues until the water addition step (S25) is completed.

[0074] <Action and effect> If the hydration step (S25) is carried out in an environment where the solvent contained in the stock solution to which the additive has been added and the water-added solution is easily volatile, gelation due to the hydrolysis and dehydration condensation reaction of the metal alkoxide is likely to occur. By cooling the stock solution to which the additive has been added and the water-added solution to low temperatures and maintaining that low temperature until the end of the hydration step (S25), it is possible to suppress the evaporation of the solvent and delay the hydrolysis and dehydration condensation reaction, resulting in a more homogeneous sol solution.

[0075] <Modification> Although the embodiment of the present invention has been described above, the present invention can be embodied in other forms.

[0076] For example, in the preparation method shown in Fig. 2, a solution cooling step may be performed in which the solutions prepared in the stock solution preparation step (S1) and the water-added solution preparation step (S2), i.e., the stock solution and the water-added solution, are cooled to a low temperature until the water addition step (S3) is completed. By performing the solution cooling step, evaporation of the solvent can be suppressed, and a more homogeneous sol solution can be obtained.

[0077] As shown in FIG. 5, the filtration step (S15) may be omitted from the coating solution preparation method shown in FIG. 3. The preparation method shown in FIG. 5 includes the additive application step (S12), which can prevent the formation of a polymer gel with a large molecular size in the mixed solution. Therefore, even if the filtration step (S15) is omitted, segregation in the coating formed on the surface of the powder particles can be prevented. However, to further reduce segregation, both the additive application step (S12) and the filtration step (S15) may be performed, as shown in FIG. 3. The stock solution preparation step (S11), the additive application step (S12), and the water-added solution preparation step (S13) may be performed in parallel, or in reverse order.

[0078] 5, a solution cooling step may be performed in which the solutions prepared in the additive application step (S12) and the water-added solution preparation step (S13), i.e., the stock solution to which the additive has been added and the water-added solution, are cooled to a low temperature until the water addition step (S14) is completed. By performing the solution cooling step, evaporation of the solvent is suppressed, and a more homogeneous sol solution can be obtained.

[0079] Alternatively, as shown in FIG. 6, the water-added solution preparation step (S13) may be omitted from the coating solution preparation method shown in FIG. 3, and in the water addition step (S14') following the additive application step (S12), moisture from the atmosphere may be incorporated into the additive-added stock solution. For example, moisture from the atmosphere may be incorporated into a lithium-niobium mixed ethoxylate solution to which ethyl acetoacetate has been added, and an inorganic polymer containing a uniform mixture of lithium and niobium may be formed through a hydrolysis-dehydration condensation reaction of a metal alkoxide. In this case, moisture is incorporated while stirring the lithium-niobium mixed ethoxylate solution under atmospheric pressure, in an atmosphere with a temperature of 10 to 40°C and a relative humidity of 10 to 100%. A relative humidity of 20 to 70% is preferable, and a relative humidity of 30 to 60% is even more preferable. By incorporating moisture into the solution at an appropriate rate, the hydrolysis-dehydration condensation reaction can proceed while suppressing segregation.

[0080] As shown in Fig. 7, instead of the water addition step (S14') shown in Fig. 6, a water addition step (S14'') may be performed in a low-temperature atmosphere. In this water addition step (S14''), the atmosphere of the stock solution to which the additive has been added is kept at a low temperature (for example, 10°C or lower).

[0081] When water is absorbed from the atmosphere into the solution (raw solution to which additives have been added), the weight of the solution increases due to the addition of water. However, at the same time, the solvent evaporates from the solution, making it difficult to estimate the amount of water added to the solution. Furthermore, as mentioned above, in the water addition step (S14'), which is carried out in an environment where the solvent contained in the solution is easily volatilized, gelation due to the hydrolysis and dehydration condensation reaction of the metal alkoxide is likely to occur. In the water addition step (S14'') under a low-temperature atmosphere, the atmosphere surrounding the solution is kept low temperature, which reduces the vapor pressure of the solvent and delays the hydrolysis and dehydration condensation reaction, resulting in a more homogeneous sol solution.

[0082] As shown in Figure 8, the water-added solution preparation step (S2) may be omitted from the coating solution preparation method shown in Figure 2, and in the water addition step (S3') after the stock solution preparation step (S1), moisture contained in the atmosphere may be incorporated into the lithium-niobium mixed ethoxy solution, which is the stock solution, and an inorganic polymer in which lithium and niobium are uniformly mixed may be formed by hydrolysis and dehydration condensation reaction of metal alkoxide in the lithium-niobium mixed ethoxy solution.

[0083] Furthermore, in the water addition step (S3') after the stock solution preparation step (S1), the atmosphere surrounding the solution may be kept at a low temperature, which allows a more homogeneous sol solution to be obtained.

[0084] Furthermore, as shown in Fig. 9, the filtration step (S15) may be omitted from the coating solution preparation method shown in Fig. 6. In the water addition step (S14') shown in Fig. 9, the atmosphere surrounding the solution may be kept at a low temperature, which allows a more homogeneous sol solution to be obtained.

[0085] Furthermore, if moisture contained in the atmosphere is taken up into the lithium-niobium mixed ethoxy solution as a stock solution, and a hydrolysis-dehydration condensation reaction of the metal alkoxide occurs, as shown in FIG. 10, the stock solution preparation step (S11) and the additive application step (S12) followed by the water-added solution preparation step (S13), the water addition step (S14), and the filtration step (S15) may be omitted from the preparation method shown in FIG. 3, and water molecules may not be actively added to the stock solution to which the additive has been applied, and the stock solution containing the additive may be used as a coating solution.

[0086] For the same reason, as shown in FIG. 11, the water-added solution preparation step (S2) and the water addition step (S3) may be omitted from the preparation method shown in FIG. 2, and water molecules may not be actively added to the stock solution prepared in the stock solution preparation step (S1), and the stock solution filtered in the filtration step (S4) may be used as the coating solution.

[0087] Furthermore, the present invention is not limited to the production of positive electrode active material powders for all-solid-state batteries, but may also be applied to the manufacturing processes of foods, medicines, cosmetics, electronic components, etc. Similarly, the particles to be targeted are not limited to those used in battery materials, and the average particle size may be other than 2 to 30 μm.

[0088] In addition, various design modifications can be made to the above-described configuration within the scope of the claims. [Explanation of symbols]

[0089] S1, S11: Stock solution preparation process S12: Additive application process S3,S3',S14,S14',S14'': Water addition process S4, S15: Filtration process S24: Solution cooling process (cooling process)

Claims

1. A method for producing a coating solution that is a base for a coating film formed on the surface of a fine particle by a sol-gel method utilizing a hydrolysis and dehydration condensation reaction of a metal alkoxide, comprising the steps of: a stock solution preparation step of preparing a stock solution containing a metal alkoxide; a hydration step of adding water molecules to the stock solution prepared in the stock solution preparation step; a filtration step of filtering the solution obtained by adding water molecules to the stock solution in the water addition step.

2. The coating solution manufacturing method according to claim 1 , further comprising an additive adding step of adding an additive containing a ligand to the stock solution prepared in the stock solution preparing step before the filtering step.

3. A method for producing a coating solution that is a base for a coating film formed on the surface of a fine particle by a sol-gel method utilizing a hydrolysis and dehydration condensation reaction of a metal alkoxide, comprising the steps of: a stock solution preparation step of preparing a stock solution containing a metal alkoxide; an additive application step of applying an additive containing a ligand to the stock solution prepared in the stock solution preparation step, The coating solution manufacturing method does not include a hydration step of adding water molecules to the solution obtained by adding the additive to the stock solution in the additive application step, and the solution is used as the coating solution.

4. 4. The method for producing a coating solution according to claim 2, wherein the additive is ethyl acetoacetate.

5. A method for producing a coating solution that is a base for a coating film formed on the surface of a fine particle by a sol-gel method utilizing a hydrolysis and dehydration condensation reaction of a metal alkoxide, comprising the steps of: a stock solution preparation step of preparing a stock solution containing a metal alkoxide; a filtration step of filtering the stock solution prepared in the stock solution preparation step, The coating solution manufacturing method does not include a hydration step of adding water molecules to the stock solution after filtration in the filtration step, and converts the stock solution into the coating solution.

6. 3. The method for producing a coating solution according to claim 1, wherein in the hydration step, water molecules are added to the raw solution by the raw solution absorbing moisture from the atmosphere.

7. 7. The method for producing a coating solution according to claim 6, wherein the water addition step is performed while the atmosphere is maintained at a predetermined low temperature.

8. The coating solution manufacturing method according to claim 1 or 2, further comprising a cooling step of cooling the stock solution prepared in the stock solution preparation step.

9. The method for producing a coating solution according to claim 8 , wherein the cooling step is continued until the water addition step is completed.

10. A method for forming a fine particle coating on the surface of powder particles, comprising: a coating solution preparation step of preparing a coating solution that is the basis of the coating; a dispersion step of introducing a slurry obtained by mixing the powder and the coating solution into a flow path and dispersing the slurry flowing through the flow path into each particle by a high-speed fluid airflow; a drying step in which the powder dispersed in the dispersing step is transported by an air current and the coating solution is dried during the transport; a collecting step of collecting the powder coated with the coating solution dried in the drying step, A coating forming method, wherein the coating solution preparation step uses the coating solution production method according to any one of claims 1 to 9.

Images