KR0123750B1 - Synthesizing method for electrolyte matrix of molten carbonate fuel cell - Google Patents

Abstract

A fabrication method of an electrolyte matrix for MCFC(melting carbonate fuel cell) is provided to improve dipping performance using taped casting method. The method comprises the steps of: preparing a suspension made of lithium aluminate by ball milling a mixing solution and a mixing carbonate; forming a green sheet of electrolyte matrix by taped casting the suspension used by a doctor blade; and sintering the green sheet of electrolyte matrix at 500-700 deg.C in order to form unit MCFC. Thereby, it is possible to improve cell performance.

Description

Manufacturing method of electrolyte matrix for molten carbonate fuel cell

1 is a schematic cross-sectional view showing the structure of a unit cell of a molten carbonate fuel cell.

2 is an electron scanning microscope (SEM) photograph of an electrolyte-matrix prepared according to the method of the present invention. (A) is an enlarged photograph of 45% of an electrolyte when no electrolyte is added.

3 is a schematic diagram of a unit cell test apparatus;

4 is a graph showing current test results of a unit cell as a current density over time.

The present invention relates to a method of manufacturing an electrolyte-matrix for a molten carbonate fuel cell, and more particularly, to a method of manufacturing an electrolyte-matrix to improve a cell performance by improving a method of impregnating an electrolyte into a matrix. will be.

A fuel cell is a new power generation system that converts energy generated by reacting fuel gas and oxidant gas directly into electric energy. Since electrical energy is generated by electrochemical reactions, not by combustion, etc., it has the advantage of generating less environmental pollutants, no noise, and higher thermal efficiency.However, evaporation of electrolytes and deterioration of materials due to operation at high temperatures There are also disadvantages. Such fuel cells include power generation facilities, power supplies for aerospace stations, power supplies for unmanned facilities at sea or coast, power supplies for fixed or mobile radios, power supplies for automobiles, power supplies for home appliances, and power supplies for leisure. We are interested in reviewing.

The fuel cell is classified into a molten carbonate electrolyte fuel cell operating at a high temperature (about 500 to 700 ° C.), a phosphate electrolyte fuel cell operating at a temperature near 200 ° C., and an alkaline electrolyte fuel cell operating at room temperature to about 100 ° C. or lower. Or a solid electrolyte fuel cell operating at a high temperature of 1000 ° C. or higher.

Molten Carbonate Fuel Cell (hereinafter abbreviated as MCFC) is a system that generates electricity by directly generating electricity by using reaction electrochemical reaction of hydrogen, carbon monoxide and oxygen. 1 shows a schematic cross-sectional view of an MCFC unit cell. In FIG. 1, a porous Ni anode (1), a Li-doped porous Ni oxide cathode (3) and a lithium aluminate matrix (2) filled with a mixed carbonate of lithium and potassium as electrolyte The battery body 4 is enclosed. A fuel gas inlet 5 is located on the positive electrode 1 side, and an oxidant gas inlet 6 is located on the negative electrode 3 side. The electrolyte contained in the matrix 2 is melt ionized at 500 to 700 ° C., which is the operating temperature of the cell, and the carbonate ions generated therein carry charge between the electrodes. That is, hydrogen or carbon monoxide as a fuel is supplied to the positive electrode 1, and oxygen and carbon dioxide used as an oxidant are supplied to the negative electrode 3, and hydrogen is consumed in the positive electrode region to generate water, carbon dioxide, and electrons. Flows to the negative electrode through the external circuit to generate the desired current.

Electrolyte-matrix is usually a mixed matrix of lithium carbonate (Li ₂ CO ₃ ) and potassium carbonate (K ₂ CO ₃ ) as an electrolyte in a γ-lithium aluminate (γ-LiAlO ₂ ) matrix plate. It is made by impregnating about 30% of the volume. The technique of impregnating electrolyte in the matrix plate has become an important factor affecting the performance of MCFC.

There are two known methods for producing a matrix plate for MCFC, a pressing method and a tape casting method. Pressing method is a method of mixing the γ-LiAlO ₂ powder of the constituents of the matrix evenly and dipping under high temperature and high pressure, it is difficult to control the thickness and can not be used to manufacture a large area plate. Tape casting method uses a blade called a doctor blade. The γ-LiAlO ₂ powder, an additive, and a solvent are mixed to form a slurry suspension, and the blade is used as a green sheet of the matrix sheet. It is a method of manufacturing a sheet, and the thickness can be adjusted and there is an advantage that a large area plate can be manufactured.

There are a number of methods for producing an electrolyte-matrix by impregnating an electrolyte in the matrix plate prepared as described above. When manufacturing a matrix plate by pressing, a method of mixing an electrolyte component with γ-LiAlO ₂ powder and dipping it is mainly used. use. In addition, when manufacturing the matrix plate by the tape casting method, after sintering the green sheet made of γ-LiAlO ₂ powder at a high temperature (about 1200 ° C.) before operating MCFC, ① the method of dispersing electrolyte powder on the matrix, ② A method of dissolving an electrolyte powder in a solvent such as alcohol or water and applying it on a matrix, and a method of mixing an electrolyte powder and an additive with a solvent to form an electrolyte plate and impregnation. However, by the method of impregnating the electrolyte externally, there is a problem that it is not only easy to impregnate the electrolyte into the matrix plate, but also the distribution of the impregnated electrolyte is uneven.

That is, in the method of manufacturing the electrolyte-matrix, it is difficult to control the thickness of the matrix plate and difficult to manufacture a large area when the pressing method is used. When using the tape casting method, it is difficult to evenly impregnate the electrolyte into the matrix plate. There is a problem.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to prepare an electrolyte-matrix for MCFC by a tape casting method, and to impregnate a larger amount of electrolyte more evenly into a matrix plate, and to separately sinter the green sheet at high temperature. It is to provide a method for producing an electrolyte-matrix for MCFC that does not need to.

MCFC electrolyte-matrix manufacturing method of the present invention for achieving the above object is a method for producing an electrolyte-matrix for MCFC comprising a matrix plate made by a tape casting method of a suspension of lithium aluminate, and impregnating a carbonate electrolyte component. In the method, the carbonate electrolyte component is added to the suspension of lithium aluminate in an amount of 45 wt% or less, mixed, tape cast, and dried to form an electrolyte-matrix green sheet, followed by sintering at a temperature of 500 to 700 ° C.

In the production method of the present invention, the low temperature sintering of the electrolyte-matrix green sheet is carried out at an operating temperature of 500 to 700 ° C, preferably about 650 ° C, which is the operating temperature of the MCFC, so as to operate in-situ It can be characterized by.

In the above production method, the carbonate electrolyte component is preferably 62/38 mol% mixed carbonate of lithium carbonate (Li ₂ CO ₃ ) and potassium carbonate (K ₂ CO ₃ ).

As mentioned above, impregnation of the electrolyte in the matrix plate is one of the important factors that determine the performance of the MCFC. Rather than the method of externally impregnating the electrolyte in the matrix plate as in the prior art, it has been found that an electrolyte-matrix prepared by mixing the electrolyte component and the matrix component γ-LiAlO ₂ powder together and making a suspension is more advantageous for impregnation. It is thought that this is because MCFC forms a three phase interface (gas / liquid / solid = fuel gas / electrolyte / Ni catalyst) which is an active site where it can react.

Hereinafter, the manufacturing method of the present invention will be described in more detail.

(1) Preparation of Lithium Aluminate Suspension Including Electrolyte

In a single or mixed solvent such as ethanol, toluene or xylene, 5 to 15% of polyvinyl butyral (PVB) as a binder, 5 to 20% of dibutyl phthalate (DBP) as a plasticizer and corn oil as a dispersant 3 Add to 6% and mix by ball milling for about 1 hour. Mixed powdered carbonate of lithium carbonate / potassium carbonate (62/38 mol%) to γ-LiAlO ₂ powder, which is a matrix powder, was added to the solution to 0 to 45% by weight, followed by ball milling and dispersion for 48 to 72 hours. To prepare.

(2) Preparation of Electrolyte-Matrix Green Sheet

With the suspension prepared above, tape casting was carried out using a doctor blade and dried in air for about one day to prepare a green sheet of electrolyte-matrix.

(3) Sintering of Green Sheet

The MCFC unit cell is manufactured by using the porous Ni electrode as the positive electrode and the Li-doped porous NiO electrode as the negative electrode together with the electrolyte-matrix green sheet prepared above. After liquid phase sintering at about 500 to 700 ° C., the operating temperature of MCFC is operated by introducing hydrogen / carbon monoxide (8/2) as fuel gas and oxygen / carbon dioxide (6/4 or 4/6) as oxidant gas. Since the sintering of the electrolyte-matrix green sheet is completed at 500 to 700 ° C., preferably about 650 ° C., the MCFC unit cell can be used in situ.

Hereinafter, the production method of the present invention will be described in more detail with reference to the following examples. However, the following examples are only examples of the present invention and do not limit the invention thereto.

Example 1

(1) Preparation of Lithium Aluminate Suspension Including Electrolyte

Ball milling for about 1 hour in a mixed solvent of ethanol, toluene and xylene with 15% polyvinyl butyral (PVB) as a binder, 20% dibutyl phthalate (DBP) as a plasticizer and 6% corn oil as a dispersant To mix. Lithium carbonate / potassium carbonate (62/38 mol%) and mixed carbonate were mixed with γ-LiAlO ₂ powder, which is a matrix powder, to 45% by weight, added to the solution, and ball milled and dispersed for 48 to 72 hours to prepare a suspension. .

(2) Preparation of Electrolyte-Matrix Green Sheet

With the suspension prepared above, tape casting was carried out using a doctor blade and dried in air for about one day to prepare a green sheet of electrolyte-matrix.

(3) Sintering of Green Sheet

The MCFC unit cell is manufactured by using the porous Ni electrode as the positive electrode and the Li-doped porous NiO electrode as the negative electrode together with the electrolyte-matrix green sheet prepared above. Nitrogen gas was introduced to both electrodes at 450cc at 300cc / min and a heating rate of 0.2 캜 / min, and then replaced with carbon dioxide gas to 650 캜. It is maintained at about 650 ° C. for about 5 to 10 hours and then operated by introducing hydrogen / carbon monoxide (8/2) as fuel gas and oxygen / carbon dioxide (6/4 or 4/6) as oxidant gas. Since the sintering of the electrolyte-matrix green sheet is completed at about 650 ° C., the MCFC unit cell can be used in situ.

Example 2

In the same manner as in Example 1, when preparing a lithium aluminate suspension containing an electrolyte, 5% PVB, 5% DBP, and 3% corn oil were added, and the mixed ratio of mixed carbonates, which were electrolytes, was 20 Prepared to be in weight percent.

FIG. 2 is an enlarged photograph showing a result of comparing and observing a surface and a cut surface of an electrolyte-matrix sintered at 650 ° C. by adding an electrolyte according to the embodiment of the present invention using a scanning electron microscope (SEM). Are 1000 times (left) and 5000 times (right) enlarged views when no electrolyte is added, and (B) is 500 times (left) and 2500 times (right) for Example 1 in which 45% of the electrolyte is added. It is an enlarged view. From here, it can be observed that a lot of electrolytes are attached around LiAlO ₂ particles.

In order to evaluate the performance characteristics of the electrolyte-matrix prepared by the method of the present invention as in the above embodiment with that prepared by the conventional electrolyte external impregnation method, the electrode area of 5 x 5 cm (25 cm 2) A unit cell test was conducted.

[Test Methods]

γ-LiAlO ₂ powder was prepared by tape casting to form a matrix plate and sintered at a high temperature of about 1200 ° C., followed by 1) dispersion of electrolyte powder on the matrix plate, and 2) electrolyte powder in a solvent such as alcohol or water. Melt and apply to the matrix plate, 3) the electrolyte-matrix prepared by mixing the electrolyte powder and additives with a solvent to make an electrolyte plate, and 4) the electrolyte-matrix prepared in Example 1 MCFC unit cells were made and tested using a porous Ni electrode having a porosity of 70% as an anode and a NiO electrode as a cathode.

3 is a schematic diagram of such a unit cell test apparatus. Here, the fuel gas and the oxidant gas inlet, the steam generator (S), the air cylinder (C) is connected to the unit cell (U), and the compressor (P) is connected through the regulator (G). Here, A, R and V mean ammeter, ohmmeter and voltmeter, respectively. Nitrogen gas was introduced into both electrodes of the unit cell U at 300 cc / min and the heating rate was 0.2 deg. C / min up to 450 deg. C, and then replaced with carbon dioxide gas and introduced at 650 deg. It is maintained at about 650 ° C. for about 5 to 10 hours and then operated by introducing hydrogen / carbon monoxide (8/2) as fuel gas and oxygen / carbon dioxide (6/4 or 4/6) as oxidant gas.

4 shows the operation results of the unit cell U tested according to the above method, and shows the current density over time. Here, at a constant voltage of 0.7 V, 2.6 mA / cm 2 for 1), 4 mA / cm 2 for 2), and 6 mA / cm 2 for 3), and 110 mA / cm 2 for 4). It can be seen. That is, the unit cell using the electrolyte-matrix prepared by the method of 1), 2) and 3) of the matrix plate to impregnate the electrolyte is in the range of very low current density, while The unit cell using the electrolyte-matrix prepared by the method is much higher current density, it can be seen that about 20 to 50 times higher than the conventional one. In addition, it can be seen that this high current density is maintained without deterioration over time. The electrolyte-matrix prepared according to Example 2 also showed an equivalent effect.

As described above, in the case of manufacturing the MCFC electrolyte-matrix by the tape casting method, the electrolyte component is mixed with the matrix component at a ratio of 45% or less to prepare a matrix suspension to make a green sheet, and then to a high temperature of 1200 ° C. According to the electrolyte-matrix production method of the present invention, which enables convenient in-situ operation by sintering liquid phase at an MCFC operating temperature of about 500 to 700 ° C. instead of sintering at, the impregnation ability of the electrolyte in the matrix is improved. In addition, there is an advantage that the current density of the MCFC manufactured using this is much higher.

Claims (4)

A method for producing an electrolyte-matrix for a molten carbonate fuel cell comprising forming a matrix plate by a tape casting method with a suspension of lithium aluminate and impregnating a carbonate electrolyte component, wherein the carbonate electrolyte component is 45% by weight in a suspension of lithium aluminate. The method of manufacturing an electrolyte-matrix for a molten carbonate fuel cell, characterized in that by adding and mixing below, tape casting and drying to make an electrolyte-matrix green sheet, and then sintering at a temperature of 500 to 700 ℃. The method according to claim 1, wherein the sintering at a temperature of 500 to 700 ° C is liquid phase sintering at an operating temperature of the molten carbonate fuel cell. The process according to claim 1 or 2, wherein the sintering temperature is about 650 ° C. The method according to claim 1 or 2, wherein the carbonate electrolyte component is a 62/38 mol% mixed carbonate of lithium carbonate (Li ₂ CO ₃ ) and potassium carbonate (K ₂ CO ₃ ).