JP2008123831A - Slurry composition for forming electrolyte holding plate, green sheet for forming electrolyte holding plate, electrolyte holding plate using them, and manufacturing method of them - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a slurry composition for forming an electrolyte holding plate for manufacturing the electrolyte holding plate made of lithium aluminate by using water solvent; to provide a green sheet for forming the electrolyte holding plate; to provide an electrolyte holding plate using them; and to provide the manufacturing method of them. <P>SOLUTION: The slurry composition for forming the electrolyte holding plate contains α-lithium aluminate, a water soluble binder, and water, and is pH 10-13. The water soluble binder is at least one kind of methylcellulose and polyvinyl alcohol. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a slurry composition for forming an electrolyte holding plate for producing an electrolyte holding plate used in a fuel cell such as a molten carbonate fuel cell (MCFC), a green sheet for forming an electrolyte holding plate, and an electrolyte using these The present invention relates to a holding plate and a manufacturing method thereof.

In the molten carbonate fuel cell (MCFC), lithium carbonate (Li ₂ CO ₃ ) and sodium carbonate (Na ₂ CO ₃ ) or potassium carbonate (K ₂ CO ₃ ) are placed on a lithium aluminate (LiAlO ₂ ) electrolyte holding plate. Consists of an electrolyte plate impregnated with a melt, an anode formed of porous nickel, a cathode formed of porous nickel oxide, an anode gas channel chamber and a cathode channel chamber for supplying a reactive gas to each electrode, and the like. Electric energy is generated at an operating temperature of 650 ° C.

  The MCFC electrolyte holding plate is used for the purpose of impregnating and holding mixed carbonates such as lithium carbonate and sodium carbonate in a temperature range of about 650 ° C. Therefore, the high holding ability, alkali resistance, and heat resistance for such mixed carbonates are used. Characteristics such as sex are required. Further, the electrolyte holding plate is required to have characteristics that prevent gas diffusion between the anode gas channel chamber and the cathode gas channel chamber and do not hinder the good ionic conductivity of the molten salt.

  In order for the electrolyte to be stably held on such an electrolyte holding plate, it does not react with carbonate, is an electrolyte holding material having a small pore size that can utilize capillary action, and has no defects such as cracks. It is necessary not to break even during operation at 650 ° C.

Currently, lithium aluminate is used as an electrolyte holding plate that satisfies such requirements. As lithium aluminate, in addition to γ-lithium aluminate (γ-LiAlO ₂ ; tetragonal crystal), α-type (rhombus system) and β-type (orthorhombic crystal) having the same composition and different structures are known. Until now, γ-LiAlO ₂ powder has been the most stable under the MCFC operating environment. However, when power generation is performed for a long time, it gradually becomes a phase transition to α-LiAlO ₂ . LiAlO ₂ has attracted attention.

  In addition, as a method of manufacturing the electrolyte holding plate, a paste method in which a mixed powder of lithium aluminate and a mixed carbonate is pressed at room temperature and sintered at around 500 ° C., or a hot press in which pressure is applied in a temperature range of 460 ° C. to 490 ° C. A matrix method in which an organic solvent that does not react with the lithium aluminate raw material powder, a binder, or the like is added, formed and sintered, and then impregnated with carbonate has been applied.

  Among these, the matrix method includes the papermaking method, doctor blade method, calender roll method, and electrophoresis method, but the doctor blade method has excellent production capacity, is easy to enlarge, and has good surface properties. It is suitable for the production of homogeneous electrolyte retaining plates. For this reason, manufacturing by the doctor blade method is mainly applied to the large area MCFC electrolyte holding plate.

  Therefore, at present, polyvinyl butyral is generally used as a binder in the case of manufacturing an electrolyte holding plate by applying the doctor blade method from the viewpoint of solubility in organic solvents, strength, stability, and adhesiveness. ing. Therefore, as long as an organic solvent is used, the slurry is flammable when the slurry is handled or the green sheet is produced, and sometimes has an explosion risk. In order to prevent the danger of ignition and explosion, explosion-proof devices must be used in all manufacturing equipment, such as eliminating the ignition source of equipment and preventing the generation of static electricity and sparks. For this reason, the manufacturing equipment is a high cost factor, and when the explosion-proof equipment is introduced, thorough safety education for workers involved in manufacturing, the installation of safety equipment, and further education are limited. There is a problem that manufacturing must be entrusted to an operator.

  Therefore, if a process that uses non-flammable non-polluting water as a solvent can be developed in manufacturing the MCFC electrolyte holding plate, the cost of the manufacturing equipment can be reduced, and the manufacturing cost can be reduced without limiting the number of manufacturing workers. A low electrolyte holding plate can be obtained.

  Here, regarding the production of the electrolyte holding plate using an aqueous solvent, for example, a manufacturing process by a doctor blade method using an aqueous solvent binder using lithium aluminum hydroxide or lithium aluminate hydrate as a main raw material is used. It has been proposed (see Patent Document 1).

However, according to this proposal, in order to produce fine particles having a large specific surface area of LiAlO _{2 in} the production process, it is necessary to perform a heat treatment at 550 ° C. to 700 ° C., which causes a cost increase. Not in.

On the other hand, in recent years, the production method of the raw material powder of α-LiAlO ₂ has been improved, and the particle structure does not change even when exposed to a high temperature in a molten salt for a long time. Excellent alkali resistance, heat resistance and high level retention Although an α-LiAlO ₂ powder production method that exhibits performance is provided, there is no example in which such α-LiAlO ₂ powder is used as a slurry in an aqueous solvent for detailed examination.

JP-A-6-290799 JP 2000-195531 A

  In view of the above-described circumstances, the present invention uses a slurry composition for forming an electrolyte holding plate, a green sheet for forming an electrolyte holding plate, and these for producing an electrolyte holding plate made of lithium aluminate using an aqueous solvent. It is an object of the present invention to provide an electrolyte holding plate and a manufacturing method thereof.

  1st aspect of this invention which solves the said subject contains alpha-lithium aluminate, a water-soluble binder, and water, It is pH10-13, The slurry composition for electrolyte holding board formation characterized by the above-mentioned It is in the thing.

  In the first aspect, by using a water-soluble binder and maintaining the pH to be alkaline, a stable slurry in which α-lithium aluminate is uniformly dispersed is obtained, and an electrolyte holding plate having a desired porosity and an average pore diameter. Can be obtained.

  According to a second aspect of the present invention, in the slurry composition for forming an electrolyte holding plate according to the first aspect, the water-soluble binder is at least one of methyl cellulose and polyvinyl alcohol. In the forming slurry composition.

  In the second aspect, by using a predetermined binder, it can be burned out at a relatively low temperature, and an electrolyte holding plate having a desired porosity and an average pore diameter can be obtained.

According to a third aspect of the present invention, in the slurry composition for forming an electrolyte holding plate according to the first or second aspect, the α-lithium aluminate is a powder having a specific surface area of 5 to 9 m ² / g. It is in the slurry composition for electrolyte holding board formation characterized by the above-mentioned.

  In the third aspect, by using α-lithium aluminate having a desired specific surface area, it is possible to obtain a slurry that is stable in an aqueous system and to obtain an electrolyte holding plate having a desired porosity and an average pore diameter. it can.

  A fourth aspect of the present invention is the slurry composition for forming an electrolyte holding plate according to any one of the first to third aspects, wherein water is contained in an amount of 150 parts by weight or less with respect to 100 parts by weight of α-lithium aluminate. The slurry composition for forming an electrolyte holding plate is characterized in that:

  In the fourth aspect, by setting the moisture content to a predetermined value, a green sheet that can be stored for a relatively long period of time without a precipitate can be obtained, and the average pore diameter can be obtained with a desired porosity. An electrolyte holding plate can be obtained.

  According to a fifth aspect of the present invention, in the slurry composition for forming an electrolyte holding plate according to any one of the first to fourth aspects, at least one of lithium carbonate and lithium carbonate hydrate is contained. It is in the slurry composition for electrolyte holding plate formation.

  In the fifth aspect, the presence of lithium carbonate or lithium carbonate hydrate keeps the pH alkaline and provides a stable slurry, and an electrolyte holding plate having a desired porosity and an average pore diameter can be obtained.

  The sixth aspect of the present invention contains at least one selected from a plasticizer, a dispersant and an antifoaming agent in the slurry composition for forming an electrolyte holding plate according to any one of the first to fifth aspects. In the slurry composition for forming an electrolyte holding plate.

  In the sixth aspect, a more uniform and more stable slurry can be obtained by containing a plasticizer, a dispersant, an antifoaming agent, etc., and an electrolyte holding plate having a desired porosity and an average pore diameter can be obtained. Obtainable.

  According to a seventh aspect of the present invention, there is provided a green sheet for forming an electrolyte holding plate, wherein the slurry composition for forming an electrolyte holding plate according to any one of the first to sixth aspects is formed into a sheet and dried. It is in.

  In the seventh aspect, a water-soluble binder is used and the pH is maintained alkaline, so that the α-lithium aluminate is formed from a stable slurry in which the α-lithium aluminate is uniformly dispersed. An electrolyte holding plate having an average pore diameter can be obtained.

  According to an eighth aspect of the present invention, the electrolyte holding plate forming green sheet according to the seventh aspect is heat-treated at 400 ° C. to 500 ° C. to burn off at least the water-soluble binder, and the porosity is 50 to 66. %, A porous body having an average pore diameter of 0.2 to 0.5 μm.

  In the eighth aspect, a green sheet formed from a stable slurry in which α-lithium aluminate is uniformly dispersed is heat-treated at 400 to 500 ° C. by using a water-soluble binder and maintaining the pH to be alkaline. As a result, a water-soluble binder or the like is burned out, and an electrolyte holding plate having a desired porosity and an average pore diameter can be obtained.

  According to a ninth aspect of the present invention, there is provided a green sheet for forming an electrolyte holding plate, wherein the slurry composition for forming an electrolyte holding plate according to any one of the first to sixth aspects is formed into a sheet and dried. It is in the manufacturing method.

  In the ninth aspect, by using a water-soluble binder and maintaining the pH to be alkaline, a stable slurry in which α-lithium aluminate is uniformly dispersed is molded and dried, so that the desired porosity can be obtained. It can be set as the green sheet which can obtain the electrolyte holding board of an average pore diameter.

  According to a tenth aspect of the present invention, the slurry composition for forming an electrolyte holding plate according to any one of the first to sixth aspects is formed into a sheet shape, and dried to obtain a green sheet for forming an electrolyte holding plate. An electrolyte holding plate manufacturing method is characterized in that at least the water-soluble binder is burned off by heat treatment at ˜500 ° C. to form a porous body.

  In the tenth aspect, a water-soluble binder is used and the pH is maintained alkaline, so that a stable slurry in which α-lithium aluminate is uniformly dispersed is formed and dried to dry the electrolyte holding plate forming green. By forming a sheet and heat-treating it at 400 to 500 ° C., the water-soluble binder and the like are burned out, and an electrolyte holding plate having an average pore diameter with a desired porosity can be obtained.

  An eleventh aspect of the present invention is the electrolyte holding plate manufacturing method according to the tenth aspect, wherein the heat treatment is performed after the green sheet for forming the electrolyte holding plate is installed in a fuel cell. It is in the manufacturing method of a holding plate.

  In the eleventh aspect, the green sheet can be heat-treated in the fuel cell to obtain a desired electrolyte holding plate.

  A twelfth aspect of the present invention is the method for producing an electrolyte holding plate according to the tenth or eleventh aspect, wherein the porous body has a porosity of 50 to 66% and an average pore diameter of 0.2 to 0.00. It is in the manufacturing method of the electrolyte holding plate characterized by being 5 micrometers.

  In the twelfth aspect, an electrolyte holding plate having a desired porosity and an average pore diameter can be obtained.

  According to the present invention, by using a water-soluble binder and maintaining the pH alkaline, a stable slurry in which α-lithium aluminate is uniformly dispersed can be obtained, and if this is molded and dried, It can be set as the green sheet which can be preserve | saved over a comparative long period, and the electrolyte holding board of an average pore diameter can be obtained with a desired porosity by heat-processing this at 400-500 degreeC. Furthermore, it is possible to manufacture an electrolyte holding plate using a non-polluting, non-polluting water solvent, and the manufacturing cost can be reduced.

  Hereinafter, the present invention will be described in detail.

  The slurry composition for forming an electrolyte holding plate of the present invention contains α-lithium aluminate, a water-soluble binder, and water, and has a pH of 10-13.

Here, α-lithium aluminate is α-type lithium aluminate, and can be produced with a powder having a BET specific surface area of 1 to 10 m ² / g, but the BET specific surface area is 5 to 9 m ^2. It is preferable to use a powder which is / g. This is because an electrolyte holding plate that is stable against water and has a desired porosity and pore diameter can be obtained. Such an α-lithium aluminate has an average particle size on the order of submicrons, and can be manufactured by, for example, a manufacturing method disclosed in Japanese Patent Application Laid-Open No. 2000-195531.

  In the present invention, water is used as a solvent without using an organic solvent. As water, deionized water, distilled water, pure water, or the like can be used.

  The water-soluble binder is a water-soluble binder, and any known binder can be used as long as it does not react with α-lithium aluminate and can be burned off at a desired temperature. Affinity with α-lithium aluminate, stability of the slurry, and those that can be burned down (also referred to as degreasing) at a temperature of 500 ° C. or less are preferably methyl cellulose or polyvinyl alcohol, Polyvinyl acetal etc. can also be used.

  The molecular weight of such a water-soluble binder is not particularly limited, but it affects the viscosity of the slurry to be formed. Therefore, if it is selected so as to have a viscosity suitable for the application and molding method of the electrolyte holding plate forming slurry. Good. As will be described later, when methylcellulose is used, methylcellulose having a polymerization degree of 4 to 1500 can be used, but it has been found that a polymerization degree of about 15 is preferable.

  The content of the water-soluble binder affects the adhesive strength between the α-lithium aluminate powders, and if it is too small, the strength when used as a green sheet tends to be insufficient. As will be described later, when methylcellulose is used, when a 2% by weight methylcellulose aqueous solution is used, it is confirmed that the adhesive strength tends to be too low. That is, although mentioned later for details, it is preferable to add about 3 to 7 weight% methylcellulose aqueous solution about 150 weight part or less with respect to 100 weight part of alpha-lithium aluminate. This is because α-lithium aluminate is prevented from agglomerating and the production efficiency of the green sheet is improved, and when a green sheet is formed, there is no inconvenience such as precipitates, which is preferable.

  Further, the content of water or a water-soluble binder affects the slurry viscosity in the same manner as the molecular weight of the water-soluble binder.

  The slurry composition for forming an electrolyte holding plate is generally manufactured by ball mill mixing or bead mill mixing in order to uniformly disperse α-lithium aluminate without aggregation. The slurry concentration is preferably such that the method can be applied. The optimum slurry viscosity for ball mill mixing is 50 to 500 mpa · s, and the optimum slurry concentration for bead mill mixing is 50 to 1000 mpa · s. However, it is more efficient to use less water solvent to produce green sheets. Therefore, it is preferable to adopt a slurry viscosity of 500 to 1000 mpa · s and employ bead mill mixing. Of course, the present invention is not limited to this, and other slurry viscosities and other mixing methods may be employed.

  The slurry composition for forming an electrolyte holding plate of the present invention may contain other additives such as a plasticizer, a dispersant, and an antifoaming agent, if necessary, but the pH is adjusted to a range of 10 to 13. Need to be.

  Depending on the production method, α-lithium aluminate may contain lithium carbonate, which is a raw material, as an impurity, thereby exhibiting alkalinity. The slurry composition for forming an electrolyte holding plate of the present invention is a mixture of a water-soluble binder and other additives that maintain this alkalinity. For example, when selecting a plasticizer, a dispersant, or an antifoaming agent, it is preferable to use a neutral or alkaline one. Moreover, although an alkali component may be added so that it may become the range of pH 10-13 of a slurry, when the stability of a slurry is considered, it is preferable to add lithium carbonate as an alkali component.

  Moreover, you may add a plasticizer to the slurry composition for electrolyte holding board formation of this invention as needed. Such a plasticizer improves the flexibility and surface smoothness of the formed green sheet, and examples thereof include glycerin.

  Moreover, you may add a dispersing agent, an antifoamer, etc. as needed. These dispersants and antifoaming agents preferably do not react with α-lithium aluminate and are alkaline or at least neutral.

  Here, the dispersing agent is effective to disperse the raw material powder to primary particles as much as possible, and bind the raw material powders in a dense state with a binder, thereby increasing the porosity, and the average The hole diameter can be reduced.

  Moreover, as a defoaming agent, the above-described decoy substance that reacts with the raw material powder is unsuitable, and it is preferable that the pH is constant regardless of the presence or absence of the raw material powder.

  Such a slurry composition for forming an electrolyte holding plate of the present invention is a slurry composition obtained by uniformly dispersing the above-mentioned raw materials. Preferably, a water-soluble binder is used as an aqueous solution, and α-lithium aluminum is used. Nate powder and other additives as required are mixed and mixed by a known method such as ball mill mixing or bead mill mixing to obtain a uniform slurry.

  The slurry composition for forming an electrolyte holding plate of the present invention can be formed into a sheet and dried to produce a green sheet for forming an electrolyte holding plate.

  Thus, in order to manufacture the electrolyte holding plate forming green sheet, it is necessary to apply and dry by various application methods. Examples of the coating method include various methods such as a doctor blade method and a spin coating method, and drying may be performed by natural drying or heat drying.

  The electrolyte-forming green sheet of the present invention has a porosity of 50 to 66% and an average pore diameter of 0.2 to 0.5 μm by heat treating at 400 ° C. to 500 ° C. to burn off at least the water-soluble binder. It can be set as the electrolyte holding plate which is a porous body. If the porosity is smaller than the above-mentioned range, the performance as a fuel cell cannot be sufficiently exhibited. On the other hand, if the porosity is larger, the performance of the fuel cell can be improved, but if it exceeds the above-mentioned range, the mechanical strength tends to be insufficient. It becomes. In addition, the smaller the average pore diameter, the better the holding power of the electrolyte such as carbonated molten salt. By having a flat pore diameter in the above-mentioned range, the carbonate can be favorably retained even during long-term operation. In any case, a high porosity is desirable from the viewpoint of increasing the voltage of the battery, and a low average pore diameter is desirable from the viewpoint of extending the life.

  Here, the heat treatment method is not particularly limited. However, since the water-soluble binder can be burned out by heat treatment at 400 ° C. to 500 ° C. to form a porous body, the fuel cell is formed by combining the anode, the cathode and the green sheet. And heat-treating in the temperature raising process of the fuel cell to form an electrolyte holding plate. Of course, the green sheet may be heat-treated in a normal manufacturing process to form an electrolyte holding plate. In this case, it goes without saying that the heat treatment may be performed at a temperature of 500 ° C. or higher.

  Hereinafter, examples will be described in detail with reference to test examples.

The α-LiAlO ₂ powder used in the following examples was manufactured by Nippon Chemical Industry (specific surface area: 5 m ² / g), and methyl cellulose having a polymerization degree of 15 was used as a water-soluble binder. Pure water was used as a solvent and mixed with a mixing ball using 99.9% alumina balls of 10 mmφ. A specific blending procedure is to prepare 3 wt%, 5 wt%, and 7 wt% water-soluble binder solution, add α-LiAlO ₂ powder to this, mix, and slurry composition for forming an electrolyte holding plate Manufactured. Moreover, the green sheet was produced from each slurry composition.

  Various adjusting agents were added to the slurry adjusted under each condition based on 40 g of raw material powder, and a green sheet was prepared with a doctor blade apparatus having a width of 150 mm and a length of about 600 mm. The doctor used a two-stage knife edge type, the first-stage doctor had a height of 3 mm, and the second-stage doctor had a height of 1.0 mm. The drying conditions were natural drying in a dry room controlled at a temperature of 23 to 25 ° C. and a humidity of 30% or less, and the drying time was 17 to 20 hours.

  Table 1 shows the formulations of Examples A1 to A7. A1 is a slurry added with 200 parts by weight of a 3% binder solution, A2 is a slurry added with 200 parts by weight of a 5% binder solution, A3 is a slurry added with 200 parts by weight of a 7% binder solution, and A4 is 3% bonded. Slurry to which 250 parts by weight of the agent solution is added, A5 is a slurry to which 150 parts by weight of the 3% binder solution is added, A6 is a slurry to which 125 parts by weight of the 3% binder solution is added, and A7 is 100% by weight of the 3% binder solution. This is a slurry with a part added. Although not shown in Table 1, the slurry contains 1 part by weight of a polymer dispersant (aqueous ammonium polycarboxylate: SN Dispersant 5468 manufactured by San Nopco), 2.5 defoamer (SN deformer 157 manufactured by San Nopco) 5 parts by weight of glycerin was added as a plasticizer.

  Table 1 shows the pH of these slurry compositions for forming an electrolyte holding plate. As a result, it was found that all the slurries exhibited pH 11-12. Moreover, the weight conversion porosity of the electrolyte holding plate manufactured from each slurry composition was a value around 60%, and the average pore diameter was 0.3 to 0.5 μm.

  Table 2 shows the formulations of Examples B1 to B11. These slurry compositions were produced in the same manner as in Examples A1 to A7.

(Test Example 1)
In Example B1 to B11, it shows the results of the slurry viscosity when mixed with the addition of alpha-LiAlO ₂ in aqueous binder solution was organized by degree of polymerization of methylcellulose in FIG.

As shown in FIG. 1, the lower the degree of polymerization of the binder solution, the lower the slurry viscosity. In the same binder solution, the lower the concentration of the slurry, the lower the viscosity. However, in any of the binder solutions, the binder concentration is low. In the case of 2% or less, it is confirmed that the adhesive force tends to weaken with respect to the LiAlO ₂ powder, which is a raw material powder, and it can be produced as a green sheet of about 0.5 m ² , but it tends to crack when the sheet moves after molding, etc. It was found that the handling property was extremely deteriorated and it was difficult to serve as a binder. Further, it was found that methylcellulose having a polymerization degree of 4 tends to be a sheet having poor handling properties due to weak adhesion to the raw material powder even in a 5% binder solution.

  There are methods such as impact / collision and shearing to disperse the raw material powder. However, since the raw material powder used in this example has an average particle size on the order of submicron, a function to loosen the agglomerated particles is required. . For this reason, a mixing method having a shearing function is required. A typical mixing method is dispersion by a ball mill. The optimum slurry viscosity for dispersion by ball mill mixing is approximately 50 to 500 mpa · s. However, since the ball mill requires a long time to stabilize the dispersion, there is a problem in that it cannot easily meet the production demand. One of the improvements, high productivity, and systematization is a mixing method using a bead mill. By using this method, a slurry viscosity of 50 to 1000 mpa · s can be handled, and dispersion can be achieved in a short time. Become. From the viewpoint of slurry mixing and defoaming, the lower the viscosity, the better. For green sheet forming and shortening the drying time, it is better to increase the viscosity (reducing the amount of solvent as much as possible). It is desirable to be about ~ 1000 mpa · s. Considering this point, it can be seen from the results shown in FIG. 1 that a 3% binder solution having a low binder concentration is a slurry composition having a viscosity most suitable for mass production by using a binder having a concentration degree of 15. I understood.

(Test Example 2)
From Examples A1 to A7, when the amount of water in the slurry was changed based on a 3% binder solution with the binder solution parts being 100 parts by weight, 125 parts by weight, 150 parts by weight, 200 parts by weight and 250 parts by weight Further, a green sheet was prepared for the slurry when the water content was 200 parts by weight and the binder concentration was changed, and the surface state was observed.

  For surface observation, each sample was cut out and subjected to gold vapor deposition, and then the surface shape was examined with an electron microscope. FIG. 2 (a) is a typical SEM photograph without flake-like precipitates, and FIG. 2 (b) is a typical SEM photograph with flake-like precipitates. This phenomenon is a phenomenon that occurs on the surface of the green sheet (dry upper surface), and was not observed under any condition on the lower surface of the sheet. As shown above, depending on the production conditions, there are cases where there are flake-like precipitates on the surface of the green sheet, and there are cases where it is not present or cannot be confirmed. It is inferred that this is a phenomenon of dissolving in water and reprecipitating on the upper surface where water evaporates during the drying process of the green sheet. The relationship between these precipitates and the number of water solvent parts is shown in FIG. As shown in FIG. 3, the precipitate does not depend on the concentration or the number of parts of the binder, and can be well organized by the number of water solvent parts in the binder solution. Or almost no confirmation. In addition, since this scaly precipitate disappears by degreasing the green sheet, it is considered that there is no problem in practical use. However, it is considered that it is desirable to suppress the precipitation phenomenon on the surface or to be controllable in the manufacturing process. In this respect, it is considered better to keep the number of water parts to 150 parts by weight or less. Thus, it became clear that the flaky precipitate deposited on the surface of the green sheet can be controlled by the number of water parts to be added.

(Test Example 3)
The following examination was performed in order to identify the flake-like precipitate deposited on the green sheet.

Substances present in the raw material powder are α-LiAlO ₂ or Li ₂ CO ₃ powder and Al ₂ O ₃ powder used when synthesizing the raw material powder. The substance having the property is considered to be α-LiAlO ₂ or Li ₂ CO ₃ powder. Therefore, the isoelectric point (pH) when LiAlO ₂ (no distinction between α, β, and γ) was dissolved in water was calculated for these two substances using FactSage (Aqualib-Web). When LiAlO ₂ completely reacts with water at 20 ° C., H ₂ O, Li ⁺ , OH ⁻ and LiOH are present in the solution as liquids, and Al ₂ O ₃ is present as a solid. The pH at that time is calculated to be 14.6. On the other hand, when Li ₂ CO ₃ reacts with water, H ₂ O, Li ⁺ , CO ₃ ²⁻ , HCO ₃ ⁻ , OH ⁻ , LiOH are present in the solution at 20 ° C., and Li ₂ CO ₃ exists as a solid. The pH at that time is calculated as 11.5.

Although this calculation is an approximate calculation, the LiAlO ₂ powder dissolution and the Li ₂ CO ₃ powder dissolution have different pH, so it is possible to examine which is the dissolved / re-deposited material by measuring the pH of the slurry. it was thought. Therefore, as shown in Table 1, the pH of the actually produced slurry is in the range of pH 11-12. From this fact, it is almost the same value as pH 11.5 calculated when Li ₂ CO ₃ is dissolved in water, and it is inferred that the dissolved species is Li ₂ CO ₃ . However, in the electrolyte holding plate that has undergone the degreasing process at 650 ° C., the scaly precipitate disappears, so that it does not exist as Li ₂ CO ₃ having a melting point near 760 ° C., but Li ₂ CO ₃ water. It is thought that it reprecipitated in the form of a Japanese product.

Here, FIG. 4 shows the results of dissolving and re-depositing Li ₂ CO ₃ reagent in water and conducting a precipitate shape confirmation test using SEM. As a result, the photograph in FIG. 4 confirms the precipitate having the same shape as in FIG. 2B, and the flake-like precipitate deposited in the green sheet is Li ₂ CO ₃ or a hydrate thereof. The possibility is high.

From the above studies, LiAlO ₂ powder has been said to react with water and grow easily so far, but α-LiAlO ₂ powder used in this test is a stable powder to water by improving the production method. In addition, Li ₂ CO ₃ mixed in the powder manufacturing process is dissolved in water as a solvent, so that the pH of the slurry is kept at an alkaline level of about 11 to 12, and the reaction between the LiAlO ₂ powder and water is suppressed. As a result, it is considered that the use of water as a solvent did not cause the growth of α-LiAlO ₂ powder.

(Test Example 4)
About each slurry composition of Example A1-A7, the relationship between the number of binder parts and the slurry viscosity before defoaming was investigated, and the result arranged by the number of binder parts is shown in FIG. The viscosity of the slurry was measured using a viscometer manufactured by Toki Sangyo Co., Ltd. (TVB-10M).

As a result, it was found that the change in the viscosity of the slurry was larger when the concentration of the binder solution was changed than when the number of parts of the 3% binder solution was changed. Further, when paying attention to the 3% binder solution, when the binder solution is 100 parts by weight (97 parts by weight of water), the slurry viscosity is about 900 mpa · s, which is considered to be the upper limit that can be dispersed by a bead mill. When mixing by a ball mill was considered, the viscosity of 500 mpa · s or less was necessary as described above, and the result that 150 parts by weight of the binder solution should be used was obtained from FIG. Furthermore, as shown in Test Example 3, in order to suppress flaky precipitates on the sheet surface, the number of water parts is required to be 150 parts by weight or less. It was found that methylcellulose having a polymerization degree of 15 is optimal, and the concentration thereof is 3% by weight, and that 150 parts by weight of the binder solution is added to the α-LiAlO ₂ powder.

(Test Example 5)
Using the dispersant shown in Table 3 below, the dispersibility of the raw material powder was evaluated. For evaluation of dispersibility, sedimentation time was evaluated using a colorimetric tube.

  In the colorimetric tube test, 10 g of raw material powder is weighed and each dispersant is added in an amount of 0.05 to 0.1 wt%. After mixing with a mixer for 15 minutes, the mixture is placed in the colorimetric tube and then a transparent layer, suspension layer (white turbid layer), precipitation layer. Was measured at regular intervals.

  As a result, as shown in Table 3, SN dispersants 5468 and 5023 had the slowest precipitation rate, followed by Nopcosanto RFA and SN dispersant 5020 in this order. Among these, Nopco Santo RFA and SN Dispersant 5023 have a strong tendency to “repell” against the carrier sheet used when the green sheet is prepared separately, and the short part tends to be difficult to fix at the time of green sheet preparation. Judged inappropriate. Therefore, for the purpose of improving this “repellency”, a small amount of a wetting agent was added to Nopcosanto RFA to evaluate the dispersibility. However, none of the results showed good results, and SN Dispersant 5468 was used as a dispersing agent. Was found to be suitable.

(Test Example 6)
About the antifoamer shown in Table 4, the antifoamer was evaluated by measuring the pH at the time of adding the pH and raw material powder.

  As a result, it was found that SN deformers 157, SN deformers 260, and SN deformers 485 are the antifoaming agents that satisfy the condition that the pH is constant regardless of the presence or absence of the raw material powder. In addition, since the slurry pH when the raw material powder and the aqueous solvent are mixed is 11.6 and basic, it is desirable that the antifoaming agent is basic. Therefore, in consideration of such points, the SN deformer 157 is medium. It was found to be suitable as an antifoaming agent because it is basic to basic and does not react with the raw material powder.

(Example C)
In each of the above-described examples, the container used was as small as 500 mL and the amount of slurry was about 100 mL, and the mixing ball was only 10 mmΦ. However, a 2 L polyethylene container was used for a large area green sheet manufacturing apparatus, and α -150 parts by weight of a 3% by weight binder solution was added to LiAlO ₂ powder, but 1 part by weight of a dispersant (SN Dispersant 5468) and 2.5 parts by weight of an antifoaming agent (SN deformer 157) in the slurry (S1) Part (S2) was added to prepare a total volume of 600 mL. The mixing balls were 10 mmφ and 5 mmφ in a 99.9% alumina ball weight ratio of 1: 2. Then, the mixture was mixed at a rotation speed of 100 rpm, and 40 mL of the slurry was taken out every 3 hours. After viscosity measurement and defoaming, the sheet was molded using a test apparatus for condition extraction. Then, degreasing and chemical analysis were performed.

A green blade was produced using a doctor blade device having a width of 600 mm and a length of 800 mm (area: about 0.5 m ² ). The doctor used a single-stage cylindrical blade, and the blade height was set so that the thickness of the green sheet was about 0.45 mm. Drying was not performed by supplying hot air or the like to the upper part of the green sheet, but an electric heater was disposed at the lower part of the sheet molding, and the set temperature was 30 ° C.

  In order to investigate the relationship between the stirring time of the slurry and the porosity of the prepared electrolyte holding plate (hereinafter referred to as the weight-converted porosity), about 40 mL of slurry was stirred every 3 h with a ball mill using 1000 mL of the slurry of Example A5. The sheet was taken out and molded, and data for up to 24 hours was acquired. The prepared sheet was degreased with an electric furnace, and the pore size distribution, average pore size, and porosity (hereinafter referred to as Hg porosimeter porosity) were measured with a mercury porosimeter (manufactured by Shimadzu Corporation, Autopore 9250).

  FIG. 6 shows the relationship between the mixing time of the slurry S1 and the transition of the formed weight-converted porosity.

  The weight-converted porosity of the electrolyte holding plate formed with 40 mL decreases as the stirring time becomes longer. However, when stirring for 18 hours or more, the weight-converted porosity shows a substantially constant value of 56%, which is the lower limit. I understood.

  On the other hand, even when a total amount of 600 mL was produced using a large area green sheet production apparatus, only a porosity of about 59% was obtained. This is because the data of every 3 hours previously performed was 600 mL of slurry at the beginning, but it was taken as a method of extracting 40 mL every 3 hours to form a sheet, so 160 mL compared to the case where the entire 600 mL was mixed for 18 hours However, since the slurry volume is decreased, it is considered that the ratio of the mixing balls and the slurry in the ball mill is changed and the dispersion of the raw material powder is advanced. However, even when the slurry is 600 mL, the porosity in terms of weight can be lowered to the lower limit of 56% by mixing for 24 hours.

  The electrolyte holding plate used here is the process of starting the weighing of raw materials and mixing with a ball mill in the evening, taking out and measuring the previously produced sheet in the next morning, and forming the green sheet in the daytime. This was optimal. In this case, it is most efficient to complete the stirring in about 21 hours. Therefore, when measures for shortening the production time were examined, mixing was performed by adjusting the additive amount of the dispersant in order to improve the dispersion performance. It has been found that the slurry viscosity can be adjusted and the mixing time can be adjusted. Thus, by adding 2 parts by weight of the dispersant, a porosity of 56% could be obtained even after stirring for 21 hours.

  FIG. 7 shows the relationship between the Hg pore diameter and the average pore diameter measured using a mercury porosimeter of the electrolyte holding plate (after degreasing) prepared with the slurry (S2). FIG. 8 shows the relationship between the Hg porosimeter porosity and the weight-converted porosity. From FIG. 7, the weight-converted porosity tends to be slightly low as the porosity, but it was confirmed that there is a good correlation with the Hg porosimeter porosity. Therefore, for the evaluation of the pore diameter of the produced member, the porosity obtained by cutting out the produced green sheet and estimating the volume and weight without performing a mercury porosimeter measurement that takes time for pretreatment such as a degreasing process. This indicates that it can be evaluated. Further, from FIG. 8, a good linear relationship is obtained between the porosity and the average pore diameter, and in order to produce an electrolyte holding plate that satisfies the target specification, an electrolyte holding having a weight-converted porosity of 55% to 59%. It was necessary to produce a plate, and the average pore diameter at that time was found to be between 0.2 and 0.3 μm.

  FIG. 9 shows the pore size distribution after degreasing. As is apparent from the figure, it was confirmed that an electrolyte holding plate having a sharp single peak around 0.2 μm was formed.

On the other hand, an electrolyte holding plate having a pore size larger than that of the electrolyte is required, and it is desirable that the average pore size is small in order to increase the holding power of the carbonate. Such viewpoint change the properties of the raw material powder from the changes from the specific surface area 5 m 2 ^{/ g} in the powder having a specific surface area of 7~10m 2 / ^g, Figure 8 shows the results of investigation also when using this . As a result, it was confirmed that the average pore diameter could be reduced to 0.2 μm while maintaining the porosity at 60%. It was also found that the porosity and average pore diameter can be adjusted by increasing the specific surface area of the raw material powder.

(Test Example 7)
The green sheet formed using the slurry S2 of Example C was degreased at 650 ° C. to form an electrolyte holding plate, and 0.5 g of this electrolyte holding plate was heated and dissolved with a mixed acid of 4 mL of concentrated phosphoric acid + 5 mL of concentrated sulfuric acid, Li and Al content rates were measured. Li was quantified by atomic absorption method, and Al was quantified by ICP analysis. In addition, XRD measurement and specific surface area measurement were performed.

FIG. 10A shows the result of measuring the amount of Li in the acid-dissolved solution. As a result, the content after the tape molding was slightly lower than that of the untreated raw material, but no difference in content depending on the tape molding conditions was observed. Moreover, although the results of both samples were significantly lower than the Li content of 10.5% calculated from the composition formula LiAlO ₂ , the cause is unknown.

  FIG. 10B shows the Al content. Differences due to tape molding conditions were observed, and TL180705-1 tended to have a high Al content. This is probably because TL180704-1 uses zirconia for the mixing balls and TL180705-1 uses alumina balls, so there was contamination from the mixing balls. Essentially, there was a large difference in the Al content. It is thought that it is not. However, although all samples are significantly lower than the calculated value (40.9%), the reason for this is unknown.

  FIG. 10C shows the Li / Al molar ratio. Although no significant difference was observed between the samples, it can be seen that all samples contained only about 80% of Li with respect to Al.

  FIG. 11 shows comparative data of specific surface area. It was found that the specific surface area of the powder after tape molding was slightly larger than that of the untreated powder. This is considered to be because the raw material powder was sufficiently dispersed by mixing with a ball mill.

  Moreover, although FIG. 12 is a diffraction pattern by XRD, about the shape of the diffraction pattern, a clear difference was not able to be confirmed between untreated powder and degreased powder after tape formation.

  From the above, the difference in powder properties between the untreated powder and the tape is slightly different in the Al content, but this is considered to be the mixing of Al from the ball. It was confirmed that no special influence was exerted on the powder by using water as a solvent.

(Example D)
Using the slurry S2 of Example C, a green sheet was prepared and installed in the fuel cell together with the electrode member, and then degreased and impregnated with carbonate during the temperature rising process of the fuel cell, and a power generation test was performed at 650 ° C. For comparison, a power generation test was similarly performed on an electrolyte plate cell using an organic solvent.

  Table 5 shows the detailed specification of the material combination of the electrolyte plate cell of this example subjected to the power generation test. The electrolyte plate cell of the comparative example was 18CI-1, and the electrolyte plate cell of the example was 18CI-2.

The electrodes used in the examples and comparative examples were both cut out from the same lot, the members having the same specifications were used, and the only different member was the electrolyte holding plate. In addition, the temperature rising process until the start of power generation is the same for both cells. Furthermore, a power generation test of about 700 hours was performed on a small cell (electrode area of about 5 cm ² ) having the same specifications as the example.

  FIG. 13 shows the performance factor analysis test results of the cell performance at the initial stage of power generation analyzed by the performance display formula developed by the present applicant.

  When the cell (18CI-1) of the comparative example using an organic solvent is compared with the water-based electrolyte plate cell (18C-2) of the example, the voltage drop due to the internal resistance is small because the thickness of the electrolyte plate is slightly thinner. The voltage drop due to other overvoltages was almost the same, and it was found that there was no difference in performance. In addition, the N2 concentration at the anode outlet due to cross leakage from the cathode is kept at a low level of about 0.5%, and the open circuit voltage is almost the same as the theoretical value. I was able to.

14 shows (a) a photograph of the electrolyte plate before the test, (b) after 700 hours of power generation, and (c) α-LiAlO ₂ raw material powder, and (d) made with an organic solvent. It is a cross-sectional SEM photograph of the electrolyte holding plate. Although it is a short time operation, there is no significant difference between the α-LiAlO ₂ particle shape before and after the test, and the particles with the electrolyte holding plate prepared using the raw material powder or the organic solvent. There was no significant difference in diameter, and it became clear that even when an electrolyte holding plate prepared using water as a solvent was used, there was no tendency for particles to enlarge or become finer in the early stage of power generation.

(Results of Examples and Test Examples)
1) The flaky precipitate present on the surface of the green sheet is inferred as Li ₂ CO ₃ or Li ₂ CO ₃ hydrate from the pH measurement of the slurry and disappears in the degreasing process. For this reason, it has become clear that there is no problem from the viewpoint of maintaining the electrolyte plate function, and that flaky precipitates can be suppressed by reducing the amount of water added to the raw material powder during slurry mixing. It was.

2) In order to produce an α-LiAlO ₂ electrolyte holding plate using an aqueous slurry, methylcellulose having a polymerization degree of about 15 is used as a binder, and an aqueous solution having a concentration of 3% by weight is used to maintain the binding force. It became clear that this was important.

  3) A dispersant is greatly involved as a means for adjusting the porosity of the electrolyte holding plate, and an anionic polycarboxylate aqueous solution is suitable for the raw material powder. It was found that neutral to basic ones are suitable to avoid reaction with the powder.

  4) The relationship between the mixing time of the slurry and the porosity of the electrolyte holding plate was clarified, and it became possible to adjust the mixing time to obtain the desired porosity by adjusting the amount of dispersant added. . Further, when this process technology is used, it is possible to produce an electrolyte holding plate in the range of porosity of 55% to 65% and average pore diameter of 0.2 μm to 0.5 μm.

  5) From the evaluation of the tape after molding and the evaluation of the particle shape of the electrolyte holding plate after the power generation test, no significant difference from the raw material powder was observed, and a good electrolyte holding plate could be produced.

  6) As a result of the power generation test using the electrolyte holding plate produced by the process using the organic solvent and the aqueous electrolyte holding plate of the present invention, it has the same good performance as the electrolyte plate cell produced using the organic solvent. In addition, it has been found that the aqueous electrolyte holding plate, which has been given up until now, is effective.

In Examples B1 to B11, which is a graph showing the results of the slurry viscosity when mixed with the addition of alpha-LiAlO ₂ in aqueous binder solution was organized by degree of polymerization of methylcellulose. It is an electron micrograph of the surface shape of an Example. It is a figure which shows the relationship between a deposit and a water-solvent part number. It is an electron micrograph to precipitate Li ₂ CO _3. It is a figure which shows the relationship between binder part number and the slurry viscosity before defoaming about each slurry composition of Example A1-A7. It is a figure which shows the transition relationship of the mixing time of the slurry of Example C, and the shape conversion porosity of the weight conversion. It is a figure which shows the relationship between the Hg void | hole diameter measured using the mercury porosimeter of the electrolyte holding plate (after degreasing) produced with the slurry (S2), and an average pore diameter. It is a figure which shows the relationship between the Hg porosimeter porosity of the electrolyte holding board (after degreasing) produced with the slurry (S2), and the weight conversion porosity. FIG. 4 is a diagram showing a pore size distribution of an electrolyte holding plate of Example C. It is a figure which shows the result of the chemical analysis of the molding tape of Test Example 7. It is a figure which shows the comparative data of the specific surface area of Test Example 7. It is a figure which shows the diffraction pattern by XRD. It is a figure which shows the performance factor analysis test result of the cell performance in the power generation initial stage of Example D. It is an electron micrograph of the electrolyte plate etc. of the small cell of an Example.

Claims (12)

A slurry composition for forming an electrolyte holding plate, comprising α-lithium aluminate, a water-soluble binder, and water, and having a pH of 10-13. The slurry composition for forming an electrolyte holding plate according to claim 1, wherein the water-soluble binder is at least one of methyl cellulose and polyvinyl alcohol. 3. The electrolyte holding plate forming slurry composition according to claim 1, wherein the α-lithium aluminate is a powder having a specific surface area of 5 to 9 m ² / g. Slurry composition. The slurry composition for forming an electrolyte holding plate according to any one of claims 1 to 3, wherein water is contained in an amount of 150 parts by weight or less with respect to 100 parts by mass of α-lithium aluminate. Slurry composition for forming. The slurry composition for forming an electrolyte holding plate according to any one of claims 1 to 4, comprising at least one of lithium carbonate and lithium carbonate hydrate. The slurry for forming an electrolyte holding plate according to any one of claims 1 to 5, comprising at least one selected from a plasticizer, a dispersant, and an antifoaming agent. Composition. A green sheet for forming an electrolyte holding plate, wherein the slurry composition for forming an electrolyte holding plate according to any one of claims 1 to 6 is formed into a sheet and dried. The green sheet for forming an electrolyte holding plate according to claim 7 is heat-treated at 400 ° C to 500 ° C to burn off at least the water-soluble binder, and has a porosity of 50 to 66% and an average pore diameter of 0.2 to An electrolyte holding plate, which is a 0.5 μm porous body. A method for producing a green sheet for forming an electrolyte holding plate, wherein the slurry composition for forming an electrolyte holding plate according to any one of claims 1 to 6 is formed into a sheet and dried. The slurry composition for forming an electrolyte holding plate according to any one of claims 1 to 6 is formed into a sheet shape, dried to obtain a green sheet for forming an electrolyte holding plate, and heat-treated at 400 ° C to 500 ° C to at least the water solution. A method for producing an electrolyte holding plate, characterized in that a porous binder is obtained by burning out a conductive binder. 11. The method for manufacturing an electrolyte holding plate according to claim 10, wherein the heat treatment is performed after the green sheet for forming the electrolyte holding plate is installed in a fuel cell. The method for producing an electrolyte holding plate according to claim 10 or 11, wherein the porous body has a porosity of 50 to 66% and an average pore diameter of 0.2 to 0.5 µm. A manufacturing method of a board.

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