KR100348718B1 - Fabrication Method of Li/Na Electrolyte Green Sheets for Molten Carbonate Fuel Cells, and Pre-treatment and Operation Method of MCFC Comprising Li/Na Electrolyte - Google Patents

Abstract

The present invention relates to an electrolyte green for a molten carbonate fuel cell (MCFC) by molding and drying a powder slurry including a Li / Na carbonate mixed powder, an ethanol solvent, a binder, a plasticizer, a dispersant, and an antifoaming agent by tape casting. It relates to a method of producing a sheet. The present invention also relates to an operating method including pretreatment of a molten carbonate fuel cell containing a Li / Na electrolyte.

According to the manufacturing method of the Li / Na electrolyte green sheet of the present invention, the use of ethanol as the solvent reduces the dissolution rate of the cathode without using a solvent harmful to the human body, reduces the loss by evaporation, and at the same time has a small coefficient of thermal expansion. A high quality Li / Na electrolyte green sheet having high ion conductivity can be produced. In addition, the pretreatment and operation of the molten carbonate fuel cell according to the operation method of the molten carbonate fuel cell containing the Li / Na electrolyte of the present invention, corrosion of the current collector plate and the separator plate made of a metal material, thereby reducing electrolyte consumption and battery performance And all the inherent advantages of the Li / Na electrolyte.

Description

Method for preparing a Li / Na electrolyte green sheet for molten carbonate fuel cell (MCFC) and pretreatment and operation method for an MCC containing a Li / Na electrolyte {Fabrication Method of Li / Na Electrolyte Green Sheets for Molten Carbonate Fuel Cells, and Pre- treatment and Operation Method of MCFC Comprising Li / Na Electrolyte}

The present invention relates to a method for producing a Li / Na electrolyte green sheet used in a molten carbonate fuel cell (hereinafter MCFC) and a method for pretreatment and operation of a fuel cell including a Li / Na electrolyte. More specifically, Li ₂ CO ₃ / Na ₂ CO ₃ (hereinafter referred to as Li / Na) using ethanol as a solvent, a method for producing a Li / Na electrolyte green sheet for a two-component alkaline molten carbonate fuel cell, and Li / Na A method of pretreatment and operation of a molten carbonate fuel cell comprising an electrolyte.

Molten carbonates Alkali carbonates used as electrolytes in fuel cells are solid at room temperature but change to molten state at 650 ° C, and the molten carbonate is formed in the matrix between the anode and the cathode. Impregnated in the micropores serves as a passage to move the carbonate ions (CO ₃ ^2- ) generated in the anode to the cathode.

The composition of the electrolyte of the molten carbonate fuel cell is very closely related to the performance and lifetime of the fuel cell. That is, the alkali carbonate electrolyte corrodes the current collector plate and the separator plate material, which consumes a large amount of electrolyte, dissolves the NiO as a cathode, and reprecides it in the matrix, resulting in short-circuit between the electrodes, thereby degrading battery performance. Battery life can be shortened.

Listing the properties of alkaline carbonate electrolytes that can have a significant impact on the performance of molten carbonate fuel cells can be summarized into the following seven:

1) ion conductivity in the matrix,

2) solubility in the reactor and diffusion in the electrolyte,

3) electrolyte distribution in the matrix and in the electrode, related to the surface tension and affinity of the electrolyte,

4) loss phenomenon of electrolyte by evaporation of alkali hydroxide formed by reaction between water vapor and alkali carbonate in anode exhaust gas,

5) reaction and corrosion of metals and alkali carbonates such as electrodes and separators, resulting in electrolyte loss and degradation of battery performance,

6) mobility of ions in the electrolyte, and

7) Dissolution and diffusion of electrodes, especially cathode materials, into the electrolyte.

As described above, since the effect of the alkali carbonate electrolyte on the performance of the molten carbonate fuel cell is very large, studies are still underway to optimize the electrolyte composition of the molten carbonate fuel cell. However, it is very difficult to obtain the optimal electrolyte composition through battery performance experiments because the composition of the electrolyte is a dependent variable determined by the physicochemical characteristics of the electrode or the matrix. Therefore, the optimum composition that satisfies all of the above listed characteristics cannot be obtained, but the most widely used electrolyte material for MCFC to date is Li / K, whose composition is 62 mol having an eutectic point. % Li ₂ CO _3/38 mole% K ₂ CO ₃ mixture.

However, Li / K mixed salts have a disadvantage in that the cathode dissolution rate is large, the electrolyte loss due to evaporation is large, the coefficient of thermal expansion is large, and the ion conductivity is low. In particular, NiO, the cathode material of MCFC, is eluted with electrolyte during cell operation, reprecipitated with Ni, and short-circuits between electrodes, which shortens battery life. In Li / K mixed salts, the cathode dissolution rate is high and pressurized conditions At higher dissolution rates.

In order to solve the drawbacks of the Li / K mixed salt electrolyte, a mixed salt of lithium carbonate (Li ₂ CO ₃ ) and sodium carbonate (Na ₂ CO ₃ ) should be used. The electrolyte characteristics of the Li / K and Li / Na eutectic mixed salts are shown in Table 1.

Electrolyte Characteristics of Li / K and Li / Na Mixed Salts with Eutectic Points characteristic 62 mol% Li / 38 mol% K 52 mol% Li / 48 mol% Na Melting point [℃] 488 501 Density (Liquid) [g / cc] 1.94 1.96 Surface tension [mN / M] 217 243 Viscosity [mN-s / m ₂ ] 4.8 5.6 Ionic Conductivity [ohm ^-1 cm ^-1 ] 1.65 2.4 Gas solubility (O ₂ ) [mol / cm ₃ atm] x10 ^-7 About 2 About 1 Hydroxide evaporation constant [atm ² ] 10 ^-13 10 ^-14 Cathode dissolution rate after 2,000 hours [mg / cm ² ] 14.6 4.6

As described above, the Li / Na mixed salt has a smaller dissolution rate of the cathode, a smaller electrolyte loss due to evaporation, a smaller thermal expansion coefficient, and a higher ion conductivity than the conventional Li / K mixed salt. In particular, nickel oxide (NiO), a cathode material of MCFC, is eluted as an electrolyte during battery operation, reprecipitated with Ni, and short-circuits between electrodes, resulting in shortening of battery life. NiO dissolution causes acid dissolution behavior. The use of Li / Na mixed salt, which is more basic than Li / K mixed salt, can significantly reduce the elution of nickel oxide.

In spite of these advantages, however, Li / K has been used as a standard electrolyte material until now because the corrosion of sodium carbonate on metal materials of stainless steel is greater than that of potassium carbonate. In addition, Li / Na electrolyte is known to show a tendency different from the conventional Li / K mixed salt in the stability of the stainless steel, which is a separator and cathode current collector material used in the actual battery. In particular, the corrosiveness of the Li / Na electrolyte is known to appear in the process of raising the molten carbonate fuel cell from room temperature to 650 ℃ operating temperature. Therefore, suitable pretreatment methods are needed to use Li / Na electrolytes in actual cells.

On the other hand, in the molten carbonate fuel cell, there are a number of methods for impregnating the electrolyte into the matrix, but the following two are considered to be suitable for the enlargement of the stack. First, there is a method of preparing a slurry by mixing carbonate powder with a matrix powder in advance in preparing a matrix and preparing the slurry in the form of a sheet, and second, a method of independently manufacturing a matrix sheet and an electrolyte sheet. Among these methods, considering the change of electrolyte composition and electrolyte injection amount, the second method, that is, the method of manufacturing the electrolyte sheet and the matrix sheet, is the most widely used, and the thickness control and the large area are easy to prepare the electrolyte in the form of a sheet. Tape casting is mainly used.

In order to manufacture the electrolyte sheet by the tape casting method, first, a slurry having a suitable composition must be prepared. The slurry is composed of an electrolyte powder, a solvent, a binder, a viscosity modifier, and the like. The slurry composition determines the workability of the slurry during casting, and the thickness and strength and cracking of the manufactured sheet.

Among the components constituting the slurry, a solvent plays an important role, and the viscosity, drying rate, and the type of the additive are determined according to the type of the solvent. Currently, toluene, methyl ethyl ketone, or a mixture of these and other solvents are generally used as a solvent for preparing a tape casting slurry. Toluene or methyl ethyl ketone solvents are easy to control because of viscosity and slow drying speed. It is suitable for casting operation, and the electrolyte sheet produced therefrom is known to have good crack quality without any cracks. In addition, US Pat. No. 5468573 used materials such as jelly, wax, and glycerin extracted from petroleum to prepare electrolyte paste. However, the solvent of the toluene system is good workability, but very harmful to the environment and the human body, glycerin and the like is too high viscosity has a problem that is not suitable for tape casting. On the other hand, a low carbon number solvent such as ethanol is harmless to the environment and the human body, but there is a problem such as cracking during the drying process when manufacturing the sheet by the tape casting method because of the fast drying speed and low viscosity. Therefore, there is a demand for a method for producing an electrolyte green sheet having excellent performance using a solvent that is harmless to the environment and the human body.

Accordingly, the present inventors have intensively researched to solve the problems of the conventional MCFC. As a result, when the slurry composition and process conditions are characterized by using ethanol, which is harmless to the environment and human body, the electrolyte composition is excellent in Li / Na electrolyte green sheet. It has been found that excellent and safe cell performance can be obtained by developing a pretreatment method capable of obtaining and controlling the corrosiveness of a molten carbonate fuel cell containing a Li / Na electrolyte, thereby completing the present invention.

It is an object of the present invention to provide a method for producing a Li / Na electrolyte green sheet for a molten carbonate fuel cell, comprising molding a Li / Na mixed carbonate slurry containing ethanol, which is harmless to the environment and human body, as a solvent by tape casting.

Another object of the present invention is to provide a pretreatment and operation method of a molten carbonate fuel cell containing a Li / Na electrolyte.

1 is a manufacturing process diagram of a Li / Na electrolyte green sheet for a molten carbonate fuel cell of the present invention.

FIG. 2 is a graph showing a voltage change with time of a unit cell including a Li / Na electrolyte. When the first curve is pretreated under Li / K pretreatment conditions, the second curve is exposed to air around the cell. In the case of pretreatment with Li / Na pretreatment conditions, the third curve is a graph showing the case of pretreatment with Li / Na pretreatment conditions of the present invention while maintaining the surroundings of the battery with nitrogen.

Hereinafter, the present invention will be described in detail.

First, according to the present invention,

Carbonate mixed powder of Li ₂ CO ₃ and Na ₂ CO ₃ , 10 to 20 parts by weight of binder, 10 to 20 parts by weight of plasticizer, 1 to 2 parts by weight of dispersant, 1 to 2 parts by weight of defoamer, and Ball milling a mixture comprising 50 to 100 parts by weight of an ethanol solvent to prepare a powder slurry,

Molding the obtained powder slurry by a tape casting method to obtain a slip molded article,

Drying the molded body at a temperature of 40-90 ° C.

Provided is a method of manufacturing a Li / Na electrolyte green sheet for a molten carbonate fuel cell.

The manufacturing process of the MCFC electrolyte green sheet of the present invention will be described in more detail with reference to FIG. 1.

In the method for producing a Li / Na electrolyte green sheet for a molten carbonate fuel cell according to the present invention, the composition of the carbonate mixed powder of Li ₂ CO ₃ and Na ₂ CO ₃ is 40 to 60 mol% of Li ₂ CO ₃ and Na ₂ CO _3. 60 to 40 mol%, and preferred compositions are 52 mol% of Li ₂ CO ₃ and 48 mol% of Na ₂ CO ₃ , which have a eutectic point.

The composition of the electrolyte slurry affects such properties as controlling the thickness of the tape casting, thickness variation, cracking during drying, shrinkage of the electrolyte sheet due to drying, and mechanical strength and flexibility of the prepared electrolyte green sheet. The range should be adjusted appropriately.

In addition, since the electrolyte green sheet is melted after the organic additive is removed and impregnated into the matrix, it is necessary to reduce the amount of the organic additive contained in the slurry if possible. An organic additive means remaining components except a solvent and carbonate powder. The total amount of the organic additive is suitably about 15 to 30% by weight based on the slurry. If it is reduced to 15% by weight or less, cracking occurs, and when it exceeds 30% by weight, it is difficult to remove the organic additive.

In the preparation of such powder slurry, preferably, the carbonate mixed powder, the plasticizer, the dispersant, the antifoaming agent, and the ethanol are first stirred for 10 to 50 hours, and then the binder is added to the mixture and stirred for 1 to 3 days.

The mixture of this composition may be ball milled to produce a stable powder slurry, and the viscosity may be adjusted while removing solvents or bubbles in the evaporator. At this time, the final viscosity of the slurry is adjusted to between 3000 and 12000 cps, preferably between 6000 and 9000 cps.

Thus, the viscosity-adjusted powder slurry is molded by tape casting to prepare slips. Generally, a doctor blade is used for such a tape casting method. The thickness of the slip produced is primarily determined by the height of the doctor blade but is affected by the speed of the doctor blade, slurry viscosity, shrinkage during drying, and the like. In consideration of this, the moving speed of the doctor blade is set.

The molded slip is dried at 40 to 90 ° C. to produce an electrolyte green sheet. If it is below 40 ° C., the drying rate is too slow. If it is above 90 ° C., cracking occurs.

However, the carbonate mixed powder of Li ₂ CO ₃ and Na ₂ CO ₃ has a very high reactivity with moisture, so that contact with moisture during the slurry manufacturing process and the drying process causes cracks or deformation of the green sheet. The solution shall be carried out in a constant temperature and humidity room, immediately dried and placed in a plastic bag, sealed and stored in the dryer.

In addition, according to the present invention,

Combining the components of a molten carbonate fuel cell comprising a Li / Na electrolyte,

At ambient temperature to 300 ° C, air is flowed to the anode portion of the fuel cell, and at 300 to 650 ° C, a carbon dioxide mixed gas containing 5 mol% of hydrogen is flown, and after reaching 650 ° C, hydrogen and carbon dioxide are reaction gases. Flowing a mixture of water and steam,

At room temperature to 450 ° C., air is flowed to the cathode portion of the fuel cell, and at 450 to 650 ° C., an inert gas or a mixed gas containing 10% or less of hydrogen and an inert gas is passed therethrough, and after reaching 650 ° C. Includes flowing a mixed gas of air and carbon dioxide, which are reaction gases,

A method of pretreatment and operation of a molten carbonate fuel cell comprising a Li / Na electrolyte is provided.

In this method, the temperature at which the gas flowing into the cathode portion of the fuel cell is replaced with an inert gas or a mixed gas containing not more than 10 mol% of hydrogen with the inert gas is 300 to 500 ° C.

As described above, when pretreating and operating a molten carbonate fuel cell containing a Li / Na electrolyte according to the present invention, the outside of the fuel cell is filled with an inert gas, such as nitrogen, argon or helium, or the inert gas is placed outside the battery. It is desirable to allow the outer surface of the cell to not be exposed to oxygen in the air.

The molten carbonate fuel cell is composed of three parts: an anode part, an electrolyte + matrix, and a cathode part, and a separator plate engraved with a gas flow path is positioned outside the anode and the cathode to support the electrolyte and the electrode element. In addition to the anode, the electrolyte + matrix, and the cathode, fuel, oxidant, and the like are assembled to form a cell, and then the reaction gas is flowed into the anode and cathode portions, respectively, to operate the battery at an operating temperature of 650 ° C. It is divided into pretreatment stage and operation stage, and pretreatment stage refers to the process of raising the temperature from room temperature to actual operating temperature of 650 ℃. In this process, the composition of gas flowing into the battery depends on the electrode type and temperature. do.

For example, looking at a pretreatment process of a fuel cell using a conventional Li / K electrolyte, the anode part is allowed to flow air at room temperature to 300 ° C, and at 300 to 650 ° C, a carbon dioxide mixed gas containing 5% hydrogen is used. Shed. When the temperature reaches 650 ° C., the operating temperature of the fuel cell, a mixture gas of hydrogen gas, carbon dioxide, and water vapor, which is a reaction gas, is flowed. On the other hand, the cathode is made to flow air at normal temperature-450 degreeC, and the carbon dioxide mixed gas containing a trace amount of oxygen is flowed at 450-650 degreeC. At this time, the outside of the fuel cell is maintained in the state exposed to air.

However, in the case of a fuel cell using a Li / Na electrolyte, such as a molten carbonate fuel cell according to the present invention, if the same pretreatment conditions as in the case of using the Li / K electrolyte are used, severe corrosion occurs in the current collector plate and the separator plate during the pretreatment process. This appears, which leads to a significant decrease in battery performance. The reason is that the corrosion reaction occurs when the metal material of stainless steel is in contact with sodium carbonate in the presence of oxygen in the 400 to 650 ° C section. Therefore, when using Li / Na electrolytes, pretreatment conditions must be changed to prevent corrosion. In the case of using a Li / Na electrolyte, the same pretreatment conditions as in the case of using a Li / K electrolyte are used for the anode portion. However, in the case of the cathode portion, air is allowed to flow at room temperature to 450 ° C., and at 450 to 650 ° C., an inert gas such as argon, nitrogen, or helium, or an inert gas and 10 mol% or less of hydrogen are contained. The mixture gas is flowed, and after reaching the operating temperature of 650 ° C., the mixed gas of air and carbon dioxide which are reaction gases is flowed.

When operating a molten carbonate fuel cell containing a mixed Li / Na salt, according to the present invention, if the inert gas nitrogen, helium or argon is blown to the cathode in the temperature range of 450 ℃ or more to prevent the initial corrosion.

At this time, even if the inert gas is supplied to the cathode portion, if the outside of the battery is exposed to air, constant battery performance can be obtained initially, but the battery performance decreases as the internal resistance IR increases. This is because the exterior of the wet-seal site is exposed to air, resulting in the growth of a corrosion layer on the wet-sealing site during the initial pretreatment. This ruptures a portion of the matrix outside of the wet seal, resulting in cross-over or electrical short-circuit of the reaction gas, thereby shortening the life of the cell. In fact, when the battery is dismantled, the inside surface of the cell is maintained in a very clean state without being corroded, but the exterior of the wet seal portion is observed that a corrosion layer grows and a part of the matrix is ruptured.

Therefore, it is important to change not only the cathode but also the outside of the battery to an inert gas atmosphere in order to prevent corrosion of the wet sealing portion. To this end, the above-mentioned method of suppressing corrosion may be used by filling an inert gas such as Ar, He, or N ₂ in the empty space between the heat insulating material and the battery, or by flowing at a predetermined flow rate to block the inflow of air. In other words, in the case of a molten carbonate fuel cell using a Li / Na electrolyte, the fuel cell may be filled with an inert gas such as nitrogen, argon, or helium or flowed out of the fuel cell even during a pretreatment process and a normal operation process at 650 ° C. It is desirable to maintain the inert gas atmosphere so that the outer surface of the battery is not exposed to oxygen in the air.

By such an operation method, it is possible to prevent electrolyte consumption and battery performance deterioration due to corrosion of the current collector and separator plates, and to take advantage of all the advantages of the original Li / Na mixed salt.

Hereinafter, the general pretreatment conditions when the battery containing the mixed Li / K salt at 650 ℃ and the pretreatment conditions according to the present invention when operating the battery containing the Li / Na mixed salt discussed above at 650 ℃ to summarize It is shown in Table 2.

Pretreatment Conditions for Molten Carbonate Fuel Cells Including Li / K and Li / Na Mixed Salts Temperature range (℃) Li / K Li / Na Anode Cathode Anode Cathode Room temperature ~ 300 air air air air 300-450 5% H ₂ -95% CO ₂ 5% H ₂ -95% CO ₂ 450-650 5% O ₂ -95% CO ₂ Ar (or He, N ₂ ) Battery Air exposure Ar (or He, N ₂ ) supply

Hereinafter, the objects and features of the present invention will become more apparent by the preferred embodiment of the present invention in conjunction with the accompanying Figures 1 and 2. Of course, the scope and content of the present invention are not limited by these examples.

<Example 1>

Manufacturing Method of Li / Na Electrolyte Green Sheet

100 g of Li ₂ CO ₃ (98%, manufactured by Junsei Chemical) and Na ₂ CO ₃ (99.0%, manufactured by Junsei Chemical) were quantified in a 52:48 molar ratio, and then placed in a ball mill to a solvent (ethanol, 99.9%). , Carlo Erba) 75 g, Dispersant (Disperbyk-110, Hoechst) 1.5 g, Plasticizer (dibutyl phthalate, Junsei Chemical) 15 g, Defoamer (DAPPO-348, San Nopco Korea) 10 g Was added. The mixture was ball milled at 100 rpm for 1 day and then ball milled again for 20 days with the addition of 20 g of a binder (polyvinyl butyral, Mowital B30H, manufactured by Hoechst).

The prepared slurry was placed in an evaporator and stirred to remove bubbles at 40 ° C. for 30 minutes, and the slurry viscosity was adjusted to 6000 cps. The slurry was molded into a slip of 1.2 mm in thickness and 55 cm in width by a tape casting device. The doctor blade moving speed was fixed at 3 cm / sec in consideration of variables such as slurry viscosity after defoaming and thickness change after drying.

The slip molded by tape casting was heat dried at 60 ° C. for 3 hours in a constant temperature and humidity room to prepare an electrolyte green sheet. Immediately after drying the green sheet was placed in a plastic bag, sealed and stored in a dryer.

On the surface of the prepared electrolyte green sheet, cracks that may occur during drying are not generally found, no bubbles or coarse particles were seen, and they were easily handled because they had moderate strength.

In addition, as a result of measuring the cell performance by mounting it on a fuel cell, it showed a high performance of 0.85 V under a current of 150 mA / cm ² , and showed the same level of battery performance as a fuel cell with a Li / K electrolyte. These measurement results are the same as the results obtained from the electrolyte prepared using the solvent of the toluene system. From the above experiments, it was found that the physical properties and the fuel cell performance of the electrolyte sheet were excellent even when the electrolyte slurry was prepared using ethanol as a solvent in preparing the Li / Na electrolyte sheet.

Comparative Example 1

Pretreatment method according to general pretreatment process of Li / K in molten carbonate fuel cell containing Li / Na electrolyte

A Li / Na mixed salt electrolyte prepared according to Example 1 was mounted on a battery with a battery configuration as shown in Table 3 below, and a pretreatment process using a general pretreatment method of a molten carbonate fuel cell including a Li / K mixed salt shown in Table 2 above. The cell performance was measured by performing a unit cell operation.

Unit cell configuration and operating conditions Anode Ni + 10% Cr matrix γ-LiAlO ₂ Cathode NiO Electrolyte 52% Li ₂ CO ₃ /48% Na ₂ CO ₃ fuel 72% H ₂ /18% CO ₂ /10% H ₂ O Oxidant 70% Air / 30% CO ₂ Temperature 650 ℃

In this case, stainless steel, which is the cathode side separator and the collector plate material, was severely corroded, and it was observed that the initial performance of the battery was very bad. The battery performance in this case is shown by the 1st curve in FIG.

<Example 2>

Pretreatment Method of Molten Carbonate Fuel Cell with Li / Na Electrolyte

In the pre-treatment method according to the invention of the molten carbonate fuel cell containing the Li / Na mixed salt electrolyte prepared according to Example 1 in the cell with a battery configuration as shown in Table 3, and shown in Table 2 Therefore, the anode was pretreated in the same manner as using the Li / K electrolyte, the cathode was allowed to flow air from room temperature to 450 ° C., and the inert gas was flowed from 450 to 650 ° C., and after reaching 650 ° C. The cell performance was measured by injecting oxygen and carbon dioxide mixed gas, which is a reaction gas, to perform a unit cell operation.

Corrosion did not occur in the metal separator plate and the collector plate, and the performance of the fuel cell was greatly improved. The battery performance in this case is shown by the 2nd curve in FIG. The performance of such a Li / Na electrolyte fuel cell is the same as that of a cell using a Li / K electrolyte.

However, even when the inert gas was supplied to the cathode side in the pretreatment process to prevent corrosion of the separator and the collector plate inside the battery, if the outside of the battery was exposed to air, constant performance was obtained until the initial 1500 hours. From now on, battery performance began to decrease gradually as the internal resistance (IR) increased, and after 1800 hours, battery performance rapidly decreased to 0.7 V or less at 150 mA / cm ² , and the battery performance was unstable. This is because the outside of the wet seal, where the electrolyte and the separator directly contact, is exposed to air, and a corrosion layer grows outside the wet seal in the range of 500 to 600 ° C. during the initial pretreatment. As a result, a portion of the matrix outside the wet seal portion was broken, resulting in cross-over or electrical short-circuit of the reactor, thus shortening the life of the battery.

Therefore, in order to prevent corrosion of the wet seal portion, it is necessary to maintain not only the cathode but also the outside of the battery in an inert gas atmosphere during the pretreatment process. In this embodiment, the fuel cell body was placed in an airtight container, and nitrogen or argon was flowed into the container to prevent the inflow of air, thereby preventing corrosion on the outer surface of the fuel cell mentioned above. The third curve of FIG. 2 shows a change in performance of the unit cell operated while the outside of the cell was maintained in a nitrogen atmosphere. As can be seen from the third curve, good battery performance of 0.8 V or more was exhibited at a current density of 150 mA / cm ² up to 3000 hours or more, and the performance degradation rate was about ²⁴ mV / 1000 h. In addition, there was no instability of battery performance. In this way, by maintaining the outside of the battery in an inert gas atmosphere, it was possible to prevent sudden drop in battery performance and to perform stable operation.

According to the manufacturing method of the Li / Na electrolyte green sheet of the present invention, the use of ethanol as the solvent reduces the dissolution rate of the cathode without using a solvent harmful to the human body, reduces the loss by evaporation, and at the same time has a small coefficient of thermal expansion. A high quality Li / Na electrolyte green sheet having high ion conductivity can be produced.

In addition, by operating the fuel cell containing the Li / Na electrolyte according to the present invention by pre-treatment, it is possible to prevent corrosion of the current collector plate and the separator plate made of a metal material, thereby reducing electrolyte consumption and battery performance, Li / Na All the inherent advantages of electrolytes are available.

Claims (9)

Li ₂ CO ₃ 40~60 mol% and Na ₂ CO ₃ of 60~40 mol% composition of Li ₂ CO ₃ and Na ₂ CO ₃ Carbonate powder mixture, the powder 100 parts by weight of binding agent 10 to 20 parts by weight of a plasticizer for the 10 to 20 parts by weight, 1 to 2 parts by weight of a dispersant, 1 to 2 parts by weight of an antifoaming agent and 50 to 100 parts by weight of an ethanol solvent, wherein the organic additives are composed of a binder, a plasticizer, a dispersant and an antifoaming agent except for the carbonate mixed powder and the solvent. Ball milling a mixture of 15-30% by weight based on the powder slurry to produce a powder slurry, Molding the obtained powder slurry by a tape casting method to obtain a slip molded article, Drying the molded body at a temperature of 40-90 ° C. A method for producing a Li / Na electrolyte green sheet for molten carbonate fuel cell, comprising a. delete The method of claim 1 wherein the composition of the carbonate mixed powder of Li ₂ CO ₃ and Na ₂ CO ₃ is 52 mol% Li ₂ CO ₃ and 48 mol% Na ₂ CO ₃ . delete The method of claim 1, wherein the preparing of the powder slurry is performed by first stirring the carbonate mixed powder, the plasticizer, the dispersant, the antifoaming agent, and the ethanol for 10 to 50 hours, and then adding the binder to the mixture for 1 to 3 days. How to be. Combining the components of a molten carbonate fuel cell comprising a Li / Na electrolyte, At room temperature to 300 ° C., air is flowed to the anode portion of the fuel cell, and at 300 to 650 ° C., a carbon dioxide mixed gas containing 5 mol% of hydrogen is flowed. After reaching 650 ° C., hydrogen and carbon dioxide are reaction gases. Flowing a mixture of water and steam, At room temperature to 450 ° C., air is flowed to the cathode portion of the fuel cell, and at 450 to 650 ° C., an inert gas or a mixed gas containing 10% or less of hydrogen and an inert gas is passed therethrough, and after reaching 650 ° C. Includes flowing a mixed gas of air and carbon dioxide, which are reaction gases, Method of pretreatment and operation of a molten carbonate fuel cell comprising a Li / Na electrolyte. The method according to claim 6, wherein the temperature of the gas flowing into the cathode portion of the fuel cell is replaced with an inert gas or a mixed gas containing 10 mol% or less of hydrogen with the inert gas in the air. The method of claim 6, wherein the outside of the fuel cell is filled with an inert gas or an inert gas is flowed outside the cell so that the outer surface of the cell is not exposed to oxygen in the air. The method of claim 6, wherein the inert gas is selected from the group consisting of argon, nitrogen and helium.