A composite cathode material and preparation method thereof and medium-low temperature solid oxide fuel cell

Abstract

The present invention provides a composite cathode material, a preparation method thereof, and a medium and low temperature solid oxide fuel cell, belonging to the technical field of solid oxide fuel cells. First, scandium nitrate, dysprosium nitrate, urea and a solvent are mixed to obtain an impregnating solution; then the cathode matrix material is impregnated in the impregnating solution, and then dried and sintered in sequence to obtain the composite cathode material. By introducing dysprosium and scandium elements into the cathode matrix material, the surface of the cathode matrix material is modified, effectively improving the stability and polarization resistance of the cathode matrix material.

Description

Technical Field

[0001] The present invention relates to the technical field of solid oxide fuel cells, and particularly to a composite cathode material, a preparation method thereof, and a medium and low temperature solid oxide fuel cell. Background Art

[0002] A solid oxide fuel cell (SOFC) is an electrochemical power generation device that directly converts chemical energy into electrical energy. Due to its high conversion efficiency and low pollution emissions, it has attracted more and more attention and research.

[0003] However, traditional solid oxide fuel cells operate at high temperatures of 800 - 1000 °C. Such high operating temperatures pose extremely high requirements for the high-temperature resistance of materials. Therefore, reducing the operating temperature of solid oxide fuel cells can greatly reduce costs and extend the service life of the battery. However, as the operating temperature decreases, the impedance of the battery cathode will increase significantly, and the performance of the battery will also decay substantially. Therefore, it is of great significance to study a composite cathode material and its preparation method to improve the performance of medium and low temperature solid oxide fuel cells. Summary of the Invention

[0004] The purpose of the present invention is to provide a composite cathode material, a preparation method thereof, and a medium and low temperature solid oxide fuel cell to solve the problem of high impedance of the cathode material in medium and low temperature solid oxide fuel cells.

[0005] To achieve the above invention purpose, the present invention provides the following technical solutions:

[0006] The present invention provides a preparation method of a composite cathode material, comprising the following steps:

[0007] (1) Mix scandium nitrate, dysprosium nitrate, urea, and a solvent to obtain an impregnation solution;

[0008] (2) Immerse the cathode matrix material in the impregnation solution, and then successively perform drying and sintering treatments to obtain the composite cathode material.

[0009] Preferably, in the step (1), the molar ratio of the total amount of scandium ions and dysprosium ions to urea is 1:1 - 20.

[0010] Preferably, in the step (1), the molar ratio of scandium nitrate to dysprosium nitrate is 3 - 6:1; the molar volume ratio of scandium nitrate to the solvent is 3 - 6 mmol:50 - 100 mL.

[0011] Preferably, in the step (1), the solvent comprises water and an organic solvent; the organic solvent is ethanol, propanol, or acetone.

[0012] Preferably, in the step (1), the volume ratio of water to the organic solvent is 2-4:1.

[0013] Preferably, in the step (2), the cathode matrix material is lanthanum strontium manganese oxide (LSM), lanthanum strontium cobalt oxide (LSC), or lanthanum strontium cobalt iron oxide (LSCF); the mass-volume ratio of the cathode matrix material to the impregnating solution is 1-3 g:50-100 mL; the impregnating temperature is 40-60 °C, and the impregnating time is 10-14 h; the drying temperature is 80-140 °C, and the drying time is 3-6 h.

[0014] Preferably, in the step (2), the sintering temperature is 600-700 °C, and the sintering time is 4-8 h.

[0015] The present invention provides a composite cathode material prepared by the above-mentioned preparation method.

[0016] The present invention also provides a medium and low temperature solid oxide fuel cell, comprising the composite cathode material prepared by the above-mentioned preparation method or the composite cathode material.

[0017] Preferably, the medium and low temperature solid oxide fuel cell uses a CaO-MgO-Al 2 O 3 -SiO 2 mixed sealing material for sealing; in the CaO-MgO-Al 2 O 3 -SiO 2 mixed sealing material, the mass ratio of CaO, MgO, Al 2 O 3 and SiO 2 is 5-7:4-6:4-6:3-5.

[0018] Advantages of the present invention:

[0019] (1) By introducing dysprosium and scandium elements into the cathode matrix material, the present invention performs surface modification on the cathode matrix material, effectively improving the stability and polarization resistance of the cathode matrix material.

[0020] (2) The present invention prepares a composite cathode material for a solid oxide fuel cell by the solution impregnation method. The preparation method is simple and does not require repeated impregnation, making it more suitable for industrial promotion and application.

[0021] (3) The present invention uses a CaO-MgO-Al 2 O 3 -SiO 2 mixed sealing material to seal the medium and low temperature solid oxide fuel cell stack, which has good sealing performance and stability. Detailed implementation mode

[0022] The present invention provides a preparation method of a composite cathode material, comprising the following steps:

[0023] (1) Mix scandium nitrate, dysprosium nitrate, urea and a solvent to obtain an impregnating solution;

[0024] (2) Immerse the cathode matrix material in the impregnating solution, and then successively perform drying and sintering treatments to obtain the composite cathode material.

[0025] In the present invention, in the step (1), the molar total amount of scandium ions and dysprosium ions and the molar ratio of urea are 1:1 to 20, preferably 1:5 to 15, and more preferably 1:10.

[0026] In the present invention, in the step (1), the molar ratio of scandium nitrate to dysprosium nitrate is 3 to 6:1, preferably 4 to 5:1; the molar volume ratio of scandium nitrate to the solvent is 3 to 6 mmol:50 to 100 mL, preferably 4 to 5 mmol:60 to 80 mL.

[0027] In the present invention, in the step (1), the solvent comprises water and an organic solvent; the organic solvent is ethanol, propanol or acetone, preferably ethanol or propanol, and more preferably ethanol.

[0028] In the present invention, in the step (1), the volume ratio of water to the organic solvent is 2 to 4:1, preferably 3:1.

[0029] In the present invention, in the step (2), the cathode matrix material is lanthanum strontium manganite (LSM), lanthanum strontium cobaltite (LSC) or lanthanum strontium cobalt ferrite (LSCF), preferably LSC or LSCF, and more preferably LSCF.

[0030] The present invention has no particular limitation on the composition of the LSM, and the conventional composition of the LSM well-known to those skilled in the art can be used. Its source can be prepared by a conventional method or purchased commercially. The LSM of the present invention is preferably La 0.75 Sr 0.25 MnO 3-δ .

[0031] The present invention has no particular limitation on the composition of the LSC, and the conventional composition of the LSC well-known to those skilled in the art can be used. Its source can be prepared by a conventional method or purchased commercially. The LSC of the present invention is preferably La 0.1 Sr 0.9 CoO 3-δ .

[0032] The present invention has no particular limitation on the composition of the LSCF, and the conventional composition of the LSCF well-known to those skilled in the art can be used. Its source can be prepared by a common method or purchased commercially. The LSCF in the present invention is preferably La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ 。

[0033] In the present invention, the mass-volume ratio of the cathode substrate material to the impregnating solution is 1-3 g: 50-100 mL, preferably 2 g: 60-80 mL.

[0034] In the present invention, the temperature of the impregnation is 40-60 °C, preferably 45-55 °C, and more preferably 50 °C; the time of the impregnation is 10-14 h, preferably 11-13 h, and more preferably 12 h; the temperature of the drying is 80-140 °C, preferably 90-130 °C, and more preferably 100-120 °C, and the time of the drying is 3-6 h, preferably 4-5 h.

[0035] In the present invention, in the step (2), the temperature of the sintering treatment is 600-700 °C, preferably 620-680 °C, and more preferably 650 °C; the time of the sintering treatment is 4-8 h, preferably 5-7 h, and more preferably 6 h.

[0036] The present invention provides a composite cathode material prepared by the above-mentioned preparation method.

[0037] The present invention also provides a medium and low temperature solid oxide fuel cell, including the composite cathode material prepared by the above-mentioned preparation method or the composite cathode material.

[0038] In the present invention, the medium and low temperature solid oxide fuel cell uses a CaO-MgO-Al 2 O 3 -SiO 2 mixed sealing material for sealing; in the CaO-MgO-Al 2 O 3 -SiO 2 mixed sealing material, the mass ratio of CaO, MgO, Al 2 O 3 and SiO 2 is 5-7: 4-6: 4-6: 3-5, preferably 6: 5: 5: 4.

[0039] In the present invention, it is preferred to use CaO, MgO, Al 2 O 3 and SiO 2After mixing evenly, a CaO-MgO-Al 2 O 3 -SiO 2 mixed sealing material is prepared by a casting method, including the following steps:

[0040] (1) Mix CaO, MgO, Al 2 O 3 and SiO 2 in a mass ratio and then perform ball milling treatment to obtain a premix;

[0041] (2) Mix the premix, an isopropanol solution of carboxymethyl cellulose, and glycerol monostearate and then perform ball milling treatment to obtain a mixed slurry;

[0042] (3) Vacuum degas the mixed slurry under stirring and then cast it into a film to obtain a CaO-MgO-Al 2 O 3 -SiO 2 mixed sealing material.

[0043] In the present invention, in the step (1), the medium for the ball milling treatment is zirconia balls with a diameter of 1 mm, the ball-to-material ratio is 3:1, the rotation speed of the ball milling treatment is 300 rpm, and the time of the ball milling treatment is 40 min.

[0044] In the present invention, in the step (2), the mass ratio of CaO, carboxymethyl cellulose, and glycerol monostearate is 1:0.05:0.02, and the mass content of carboxymethyl cellulose in the isopropanol solution of carboxymethyl cellulose is 4%.

[0045] In the present invention, in the step (2), the medium for the ball milling treatment is zirconia balls with a diameter of 1 mm, the ball-to-material ratio is 3:1, the rotation speed of the ball milling treatment is 400 rpm, and the time of the ball milling treatment is 10 h.

[0046] In the present invention, it is preferably to use the composite cathode material, electrolyte, and anode to make a single cell, and then stack the single cell, CaO-MgO-Al 2 O 3 -SiO 2 mixed sealing material, and a metal connector as repeating units to form a medium-temperature and low-temperature solid oxide fuel cell stack, and then perform sealing.

[0047] In the present invention, the pressure of the sealing is 0.1 - 0.5 Mpa, preferably 0.2 - 0.4 Mpa, and more preferably 0.3 Mpa; the temperature of the sealing is 850 - 900 °C, preferably 860 - 880 °C, and more preferably 870 °C.

[0048] The technical solution provided by the present invention will be described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0049] In the embodiment of the present invention, the preparation method of the CaO-MgO-Al 2 O 3 -SiO 2 mixed sealing material is as follows: CaO, MgO, Al 2 O 3 and SiO 2 are mixed according to a mass ratio of 6:5:5:4, and then placed in a ball mill jar. Zirconia balls with a diameter of 1 mm (ball-to-material ratio is 3:1) are used to ball mill at a speed of 300 rpm for 40 min to obtain a premix; the premix, an isopropanol solution of carboxymethyl cellulose, and glycerol monostearate (where the mass ratio of CaO, carboxymethyl cellulose, and glycerol monostearate is 1:0.05:0.02, and the mass content of carboxymethyl cellulose in the isopropanol solution of carboxymethyl cellulose is 4%) are mixed, and zirconia balls with a diameter of 1 mm (ball-to-material ratio is 3:1) are used to ball mill at a speed of 400 rpm for 10 h to obtain a mixed slurry; the mixed slurry is stirred at a speed of 500 rpm and degassed under a vacuum condition of 4.5 Kpa for 20 h, and finally cast into a film to obtain the CaO-MgO-Al 2 O 3 -SiO 2 mixed sealing material.

[0050] Example 1

[0051] 4 mmol of scandium nitrate, 1 mmol of dysprosium nitrate, and 50 mL of solvent (a mixture of deionized water and absolute ethanol in a volume ratio of 3:1) are mixed evenly, and then urea (the molar ratio of the total amount of scandium ions and dysprosium ions to urea is 1:10) is added and mixed evenly to obtain an impregnation solution.

[0052] 1 g of La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ powder is impregnated in the above-prepared impregnation solution, impregnated at 50 °C for 12 h, taken out and dried in a constant-temperature drying oven at 120 °C for 3 h after impregnation is completed, and then placed in a muffle furnace and sintered at 650 °C for 5 h, and finally ground at a speed of 500 rpm for 3 h to obtain a composite cathode material, denoted as LSCF-Sc-Dy.

[0053] 10 g of LSCF-Sc-Dy and 15 g of rosin alcohol-ethyl cellulose solvent (the mass ratio of rosin alcohol to ethyl cellulose is 95:5) are mixed evenly to obtain a cathode slurry.

[0054] Symmetric cell preparation: GDC (Gd 0.1 Ce 0.9 O 1.9 ) powder was used. It was pressed into a 15-mm circular wafer by a tablet press and then sintered in a high-temperature furnace at 1400 °C for 5 h to obtain an electrolyte tablet. The above-mentioned cathode slurry was coated on both sides of the electrolyte tablet (coating thickness: 50 μm), dried at 120 °C, and then calcined at 1000 °C for 1 h to prepare a symmetric cell.

[0055] Single cell preparation: A commercial Ni-YSZ|YSZ anode was used to make an electrolyte film half-cell. The cathode slurry was coated on the electrolyte layer (coating thickness: 50 μm), dried at 120 °C, and finally calcined at 1000 °C for 1 h.

[0056] According to the single cell, CaO-MgO-Al 2 O 3 -SiO 2 mixed sealing material and SUS430 metal connector were used as repeating units to stack and construct a medium and low temperature solid oxide fuel cell stack, and then sealing was completed under a pressure of 0.3 Mpa and a temperature of 870 °C.

[0057] Example 2

[0058] 6 mmol of scandium nitrate, 1 mmol of dysprosium nitrate, and 100 mL of solvent (a mixture of deionized water and absolute ethanol in a volume ratio of 4:1) were mixed evenly, and then urea (the molar ratio of the total amount of scandium ions and dysprosium ions to urea was 1:20) was added and mixed evenly to obtain an impregnation solution.

[0059] 2 g of La 0.1 Sr 0.9 CoO 3-δ powder was impregnated in the above-prepared impregnation solution, impregnated at 40 °C for 14 h, taken out after impregnation and dried in a constant-temperature drying oven at 140 °C for 4 h, then placed in a muffle furnace and sintered at 600 °C for 8 h, and finally ground at a speed of 500 rpm for 3 h to obtain a composite cathode material, denoted as LSC-Sc-Dy.

[0060] 10 g of LSC-Sc-Dy and 15 g of rosin alcohol-ethyl cellulose solvent (mass ratio of rosin alcohol to ethyl cellulose is 95:5) were mixed evenly to obtain a cathode slurry.

[0061] Symmetric cell preparation: GDC (Gd 0.1 Ce 0.9 O 1.9) The powder was pressed into a 15-mm round tablet using a tableting machine and sintered in a high-temperature furnace at 1400 °C for 5 h to obtain an electrolyte tablet. The above-mentioned cathode slurry was coated on both sides of the electrolyte tablet (coating thickness: 50 μm), dried at 120 °C, and then calcined at 1000 °C for 1 h to prepare a symmetrical cell.

[0062] Single cell preparation: A commercial Ni-YSZ|YSZ anode was used to fabricate a half-cell with an electrolyte film. The cathode slurry was coated on the electrolyte layer (coating thickness: 50 μm), dried at 120 °C, and finally calcined at 1000 °C for 1 h.

[0063] According to the single cell, CaO-MgO-Al 2 O 3 -SiO 2 The mixed sealing material and SUS430 metal connector were stacked as repeating units to construct a medium-temperature and low-temperature solid oxide fuel cell stack, and then sealed at a pressure of 0.3 Mpa and a temperature of 870 °C.

[0064] Example 3

[0065] 3 mmol of scandium nitrate, 1 mmol of dysprosium nitrate, and 80 mL of solvent (a mixture of deionized water and absolute ethanol in a volume ratio of 2:1) were mixed evenly, and then urea was added (the molar ratio of the total amount of scandium ions and dysprosium ions to urea was 1:1). After mixing evenly, an impregnation solution was obtained.

[0066] 3 g of La 0.75 Sr 0.25 MnO 3-δ The powder was impregnated in the above-prepared impregnation solution, impregnated at 60 °C for 10 h, taken out and dried in a constant-temperature drying oven at 80 °C for 6 h after impregnation, then placed in a muffle furnace and sintered at 700 °C for 8 h, and finally ground at a speed of 500 rpm for 3 h to obtain a composite cathode material, denoted as LSM-Sc-Dy.

[0067] 10 g of LSM-Sc-Dy and 15 g of rosin alcohol-ethyl cellulose solvent (mass ratio of rosin alcohol to ethyl cellulose is 95:5) were mixed evenly to obtain a cathode slurry.

[0068] Symmetrical cell preparation: GDC (Gd 0.1 Ce 0.9 O 1.9 ) powder was pressed into a 15-mm round tablet using a tableting machine and sintered in a high-temperature furnace at 1400 °C for 5 h to obtain an electrolyte tablet. The above-mentioned cathode slurry was coated on both sides of the electrolyte tablet (coating thickness: 50 μm), dried at 120 °C, and then calcined at 1000 °C for 1 h to prepare a symmetrical cell.

[0069] Single cell preparation: A half cell with an electrolyte film was made using a commercial Ni-YSZ|YSZ anode. A cathode paste was coated on the electrolyte layer (coating thickness: 50 μm), dried at 120 °C, and finally calcined at 1000 °C for 1 h.

[0070] According to the single cell, CaO-MgO-Al 2 O 3 -SiO 2 The mixed sealing material and SUS430 metal connector were stacked as repeating units to form a medium and low temperature solid oxide fuel cell stack, and then sealed was completed under a pressure of 0.3 Mpa and a temperature of 870 °C.

[0071] Comparative Example 1

[0072] The difference from Example 1 was that dysprosium nitrate was not added to the impregnation solution to obtain a composite cathode material, denoted as LSCF-Sc, and other conditions were the same.

[0073] Comparative Example 2

[0074] The difference from Example 1 was that the sintering temperature was 500 °C when preparing the composite cathode material to obtain a composite cathode material, denoted as LSCF-Sc-Dy-500, and other conditions were the same.

[0075] Comparative Example 3

[0076] The difference from Example 1 was that the sintering temperature was 800 °C when preparing the composite cathode material to obtain a composite cathode material, denoted as LSCF-Sc-Dy-800, and other conditions were the same.

[0077] Comparative Example 4

[0078] La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ The powder was mixed evenly with 15 g of rosin alcohol-ethyl cellulose solvent (mass ratio of rosin alcohol to ethyl cellulose: 95:5) to obtain a cathode paste.

[0079] Symmetric cell preparation: GDC (Gd 0.1 Ce 0.9 O 1.9 ) powder was used. It was pressed into a 15 mm round tablet by a tablet press and sintered in a high temperature furnace at 1400 °C for 5 h to obtain an electrolyte tablet. The above-mentioned cathode paste was coated on both sides of the electrolyte tablet (coating thickness: 50 μm), dried at 120 °C, and then calcined at 1000 °C for 1 h to prepare a symmetric cell.

[0080] Comparative Example 5

[0081] Mix 10 g of La 0.1 Sr 0.9 CoO 3-δ powder with 15 g of rosin alcohol - ethyl cellulose solvent (the mass ratio of rosin alcohol to ethyl cellulose is 95:5) evenly to obtain the cathode paste.

[0082] Preparation of symmetrical cell: Use GDC (Gd 0.1 Ce 0.9 O 1.9 ) powder. Use a tablet press to press it into a 15 - mm round tablet, and sinter it in a high - temperature furnace at 1400 °C for 5 h to obtain the electrolyte tablet. Coat the above - mentioned cathode paste (coating thickness is 50 μm) on both sides of the electrolyte tablet, dry it at 120 °C, and then calcine it at 1000 °C for 1 h to prepare the symmetrical cell.

[0083] Comparative Example 6

[0084] Mix 10 g of La 0.75 Sr 0.25 MnO 3-δ with 15 g of rosin alcohol - ethyl cellulose solvent (the mass ratio of rosin alcohol to ethyl cellulose is 95:5) evenly to obtain the cathode paste.

[0085] Preparation of symmetrical cell: Use GDC (Gd 0.1 Ce 0.9 O 1.9 ) powder. Use a tablet press to press it into a 15 - mm round tablet, and sinter it in a high - temperature furnace at 1400 °C for 5 h to obtain the electrolyte tablet. Coat the above - mentioned cathode paste (coating thickness is 50 μm) on both sides of the electrolyte tablet, dry it at 120 °C, and then calcine it at 1000 °C for 1 h to prepare the symmetrical cell.

[0086] Performance test:

[0087] (1) Electrochemical impedance test: Conduct electrochemical impedance tests on the symmetrical cells prepared in Examples 1 - 3 and Comparative Examples 1 - 4. When testing, the applied perturbation voltage is 5 mV, and the frequency range is 50 mHz - 1 MHz. The test is carried out in an air atmosphere at 600 °C. The test results are shown in Table 1.

[0088] Table 1 Electrochemical impedance test results

[0089] Number <![CDATA[Impedance at 600 °C (Ωcm 2 )]]> Example 1 0.038 Example 2 0.056 Example 3 0.38 Comparative Example 1 0.12 Comparative Example 2 0.089 Comparative Example 3 0.076 Comparative Example 4 0.18 Comparative Example 5 0.098 Comparative Example 6 0.72

[0090] It can be seen from Table 1 that the composite cathode materials doped with scandium and dysprosium through impregnation treatment have reduced the polarization impedance of the cathode to varying degrees.

[0091] (2) Leakage rate test of medium - and low - temperature solid oxide fuel cells

[0092] Measurement principle: By measuring the inlet and outlet flow rates of fuel gas (or air), the leakage rate of the fuel cell stack is calculated, and the calculation formula is as follows:

[0093]

[0094] In the formula:

[0095] V 1 —— Inlet flow rate of fuel gas (or air), mL·min -1 ;

[0096] V 2 —— Outlet flow rate of fuel gas (or air), mL·min -1 ;

[0097] C—— Perimeter of the cell, cm;

[0098] L—— Leakage rate, cm 3 ·min -1 ·cm -1 ;

[0099] The medium and low temperature solid oxide fuel cell stacks of Examples 1 to 3 were tested under the following conditions: pressure of 0.1 Mpa, ventilation pressure of 6.89 Kpa, and after 10 thermal cycles at 800 °C. The leakage rates of Examples 1 to 3 were 0.0015 cm 3 ·min -1 ·cm -1 、0.0017 cm 3 ·min -1 ·cm -1 、0.0018 cm 3 ·min -1 ·cm -1 .

[0100] By testing the leakage rate, it can be seen that the CaO-MgO-Al 2 O 3 -SiO 2 mixed sealing material provided by the present invention has good sealing performance and stability.

[0101] As can be seen from the above examples, the present invention provides a composite cathode material, a preparation method thereof, and a medium and low temperature solid oxide fuel cell. First, scandium nitrate, dysprosium nitrate, urea, and a solvent are mixed to obtain an impregnation solution; then the cathode matrix material is impregnated in the impregnation solution, and then dried and sintered in sequence to obtain the composite cathode material. By introducing dysprosium and scandium elements into the cathode matrix material, the surface of the cathode matrix material is modified, effectively improving the stability and polarization resistance of the cathode matrix material.

[0102] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a composite cathode material, characterized in that: The steps include: (1) mixing scandium nitrate, dysprosium nitrate, urea and a solvent to obtain an impregnation solution; (2) immersing the cathode substrate material in an impregnation solution, and then sequentially performing drying and sintering treatments to obtain a composite cathode material; The molar ratio of scandium nitrate to dysprosium nitrate is 3 to 6:1; The cathode matrix material is lanthanum strontium manganese oxide, lanthanum strontium cobalt oxide or lanthanum strontium cobalt iron oxide.

2. The preparation method according to claim 1, characterized in that: In the step (1), the molar ratio of the total amount of scandium ions and dysprosium ions to urea is 1:1-20.

3. The preparation method according to claim 1 or 2, characterized in that: In the step (1), the molar volume ratio of scandium nitrate to solvent is 3-6 mmol:50-100 mL.

4. The preparation method according to claim 3, characterized in that: In the step (1), the solvent comprises water and an organic solvent; the organic solvent is ethanol, propanol or acetone.

5. The preparation method according to claim 4, characterized in that: In the step (1), the volume ratio of water to the organic solvent is 2 to 4:

1.

6. The preparation method according to claim 2, 4 or 5, characterized in that: In the step (2), the mass volume ratio of the cathode matrix material and the impregnation solution is 1-3 g: 50-100 mL; the impregnation temperature is 40-60° C., and the impregnation time is 10-14 h; the drying temperature is 80-140° C., and the drying time is 3-6 h.

7. The preparation method according to claim 6, characterized in that: In the step (2), the sintering temperature is 600-700° C. and the sintering time is 4-8 hours.

8. The composite cathode material obtained by the preparation method according to any one of claims 1 to 7.

9. A medium-low temperature solid oxide fuel cell, characterized in that: A composite cathode material obtained by the preparation method according to any one of claims 1 to 7 or a composite cathode material according to claim 8.

10. The medium and low temperature solid oxide fuel cell according to claim 9, characterized in that: The medium-low temperature solid oxide fuel cell is sealed with a CaO-MgO-Al2O3-SiO2 mixed sealing material; in the CaO-MgO-Al2O3-SiO2 mixed sealing material, the mass ratio of CaO, MgO, Al2O3 and SiO2 is 5-7:4-6:4-6:3-5.

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