Nickel-based composite electrode and preparation method thereof

Abstract

The invention discloses a nickel-based composite electrode and a preparation method thereof, and belongs to the technical field of solid oxide batteries. The preparation method comprises the following steps: molding a mixture containing a nickel compound and an electrolyte to obtain a nickel-based composite electrode precursor; and pre-sintering the nickel-based composite electrode precursor, then carrying out high-temperature flash sintering at 1500-3000 DEG C, and then carrying out annealing to obtain the nickel-based composite electrode. According to the invention, nickel enrichment at the grain boundary in the electrode can be inhibited, and the conductivity of the electrode can be improved.

Description

A nickel-based composite electrode and its preparation method Technical Field

[0001] This invention relates to a nickel-based composite electrode and its preparation method, belonging to the field of solid oxide battery technology. Background Technology

[0002] Solid oxide batteries (SOCs) are all-solid-state ceramic devices that function as both solid oxide fuel cells (SOFCs) and solid oxide electrolyzers (SOECs). SOFCs can convert the chemical energy of H2, natural gas, and hydrocarbons into electrical energy, while SOECs can convert and store solar, wind, and other renewable energy sources into hydrogen fuel.

[0003] SOCs mainly consist of an anode, a cathode, and an electrolyte. The most commonly used material for the fuel electrode (i.e., the anode) of SOCs is a nickel-based composite material, including nickel metal with oxygen ion conductor yttrium-stabilized zirconium oxide (YSZ), gadolinium oxide-doped cerium oxide (GDC), or proton conductor BaZr. 0.1 Ce 0.7 Y 0.2 O 3-δ (BZCY) fuel electrodes with mixed sintering structure have a wide range of applications.

[0004] However, severe nickel diffusion is a common problem in fuel electrodes during high-temperature sintering. For example, microstructural characterization revealed significant Ni enrichment at the YSZ grain boundaries of the SOFC anode support in fuel cells. This makes the grain boundaries a major factor in blocking oxygen ion transport, significantly reducing the overall ionic conductivity and performance of the fuel electrode.

[0005] CN117438624A discloses a method for modifying solid oxide fuel cells, wherein the anode modification steps are as follows: (1) La2O3, CaCO3, TiO2, and NiO raw materials are ball-milled with zirconia balls using ethanol as a medium. After the ethanol is evaporated by heating, the fully mixed powder is subjected to a two-stage high-temperature heat treatment. The two-stage high-temperature heat treatment is first performed at 1100℃ for 20h, and then at 1350℃ for 20h to obtain a single-phase LCTN electrode substrate; (2) The quartz chamber is evacuated, and in an H2 / N2 atmosphere, the obtained LCTN single-phase electrode substrate is excited by a thermal stimulation method in the quartz chamber using carbon paper as a heating source. The thermal stimulation method is performed at 1400℃ for 10s, and metallic Ni nanoparticles appear on the LCTN surface. This method uses short-time thermal stimulation to inhibit the growth and coarsening of Ni metal particles, thereby obtaining Ni nanoparticles with high particle density and high active site concentration. This paper does not investigate whether the short-duration thermal stimulation method used can suppress nickel enrichment at grain boundaries.

[0006] Developing novel nickel-based composite electrodes and their preparation methods to suppress nickel enrichment at grain boundaries has become one of the urgent problems to be solved in this field. Summary of the Invention

[0007] To address the aforementioned technical problems, the present invention aims to provide a nickel-based composite electrode and its preparation method. The present invention can suppress nickel enrichment at grain boundaries in the electrode, thereby improving the electrode's conductivity.

[0008] To achieve the above objectives, the first aspect of the present invention provides a method for preparing a nickel-based composite electrode, comprising the following steps: (1) molding a mixture containing a nickel compound and an electrolyte to obtain a nickel-based composite electrode precursor; (2) pre-firing the nickel-based composite electrode precursor, then flash-firing it at 1500~3000°C, and then annealing it to obtain the nickel-based composite electrode.

[0009] According to a specific embodiment of the present invention, preferably, in step (1), the nickel compound includes nickel oxide (NiO) and the like.

[0010] According to a specific embodiment of the present invention, preferably, in step (1), the electrolyte is an electrolyte for a solid oxide battery. More preferably, the electrolyte includes one or more of yttrium-stabilized zirconium oxide (YSZ), gadolinium-doped cerium oxide (GDC), scandium-stabilized zirconium oxide (ScSZ), samarium-doped cerium oxide (SDC), and perovskite oxides. Even more preferably, the electrolyte includes yttrium-stabilized zirconium oxide and / or gadolinium-doped cerium oxide.

[0011] According to a specific embodiment of the present invention, preferably, in step (1), the mass ratio of the nickel compound to the electrolyte is (10~80):(90~20).

[0012] According to a specific embodiment of the present invention, preferably, in step (2), the pre-firing temperature is 400~600℃, the pre-firing time is 1~3h, and the pre-firing is carried out in an oxidizing gas atmosphere.

[0013] According to a specific embodiment of the present invention, preferably, in step (2), the high-temperature flash burning time is 1~60s.

[0014] According to a specific embodiment of the present invention, preferably, in step (2), the high-temperature flash burning is achieved by Joule heating.

[0015] According to a specific embodiment of the present invention, preferably, in step (2), the high-temperature flash calcination includes: heating to 1500-3000°C at a heating rate of 20-500°C / s, maintaining the temperature at 1500-3000°C for 1-60s for high-temperature flash calcination, and then cooling to room temperature at a cooling rate of 100-1000°C / s. More preferably, the high-temperature flash calcination includes the following process: placing the pre-calcined product in the middle of the carbon material, applying an electric current to the carbon material, controlling the heating rate to be 20-500°C / s, heating to 1500-3000°C and maintaining the temperature for 1-60s for high-temperature flash calcination, then stopping the application of the electric current, and cooling to room temperature at a cooling rate of 100-1000°C / s to obtain the product after high-temperature flash calcination.

[0016] According to a specific embodiment of the present invention, preferably, in step (2), the annealing temperature is 300~1400℃, the annealing time is 0.5~20h, and the annealing is carried out in an oxidizing gas atmosphere.

[0017] A second aspect of the present invention provides a nickel-based composite electrode, which is prepared by the above-described method for preparing a nickel-based composite electrode.

[0018] According to a specific embodiment of the present invention, preferably, the difference between the Ni element content at the grain boundaries of the electrolyte and the Ni element content in the grains of the nickel-based composite electrode is less than 6%.

[0019] According to a specific embodiment of the present invention, preferably, the Ni content in the electrolyte grains of the nickel-based composite electrode is 1-15%.

[0020] The present invention has at least the following beneficial effects: It can suppress nickel enrichment at grain boundaries in the electrode, thereby improving the ionic conductivity at the grain boundaries. Simultaneously, the electrolyte grains in the nickel-based composite electrode of the present invention can have a high nickel content, significantly increasing both ionic and electronic conductivity, exhibiting characteristics of a mixed ionic conductor. Therefore, the nickel-based composite electrode of the present invention has improved conductivity and overall performance. Furthermore, compared to existing sintering methods, the present invention also has advantages such as simple process, short sintering time, high efficiency, and reduced energy consumption. Attached Figure Description

[0021] Figure 1 shows the STEM-HAADF images and EDS-mapping images of the grains and grain boundaries of the two nickel-based composite electrodes prepared in Example 1.

[0022] Figure 2 shows the STEM-HAADF image and EDS-mapping image of the YSZ grain boundaries of a commercially available SOFC anode support.

[0023] Figure 3 shows the electrochemical impedance spectra of 20N-YSZ from Comparative Example 3 and 20N-YSZ-UHS-800 and 20N-YSZ-UHS-1200 from Example 1, obtained by testing at 200℃ and 800℃ respectively.

[0024] Figure 4 shows the STEM-HAADF and EDS-mapping images of the nickel-based composite electrode in Example 2 at the grains and grain boundaries, as well as the electrochemical impedance spectra of the 20N-GDC of Comparative Example 4 and the nickel-based composite electrode of Example 2, which were tested at 200℃ and 800℃ respectively.

[0025] Figure 5 shows the STEM-HAADF and EDS-mapping images of the nickel-based composite electrode in Example 3 at the grains and grain boundaries, as well as the electrochemical impedance spectroscopy obtained at 250°C.

[0026] Figure 6 shows the STEM-HAADF and EDS-mapping images of the nickel-based composite electrode in Example 4 at the grains and grain boundaries, as well as the electrochemical impedance spectroscopy obtained at 250°C.

[0027] Figure 7 shows the STEM-HAADF and EDS-mapping images of the nickel-based composite electrode in Comparative Example 1 at the grains and grain boundaries, as well as the electrochemical impedance spectroscopy obtained at 250 °C.

[0028] Figure 8 shows the STEM-HAADF and EDS-mapping images of the nickel-based composite electrode in Comparative Example 2 at the grains and grain boundaries, as well as the electrochemical impedance spectroscopy obtained at 250 °C. Detailed Implementation

[0029] To provide a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the present invention will now be described in detail below, but this should not be construed as limiting the scope of the invention.

[0030] It should be noted that, unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0031] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0032] It should be understood that the terms “comprising,” “including,” and / or “containing” as used herein specify the presence of the stated features, integers, steps, components, or combinations thereof, but do not exclude the presence or addition of one or more other features, integers, steps, components, or combinations thereof.

[0033] In the ranges disclosed in the present invention, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in the present invention.

[0034] According to a specific embodiment of the first aspect of the present invention, the present invention provides a method for preparing a nickel-based composite electrode, which includes the following steps: (1) shaping a mixture containing a nickel compound and an electrolyte to obtain a nickel-based composite electrode precursor; (2) pre-burning the nickel-based composite electrode precursor, then performing high-temperature flash burning at 1500 - 3000 °C, and then annealing to obtain the nickel-based composite electrode.

[0035] In some embodiments, in step (1), the nickel compound includes nickel oxide (NiO), etc.

[0036] In some embodiments, in step (1), the electrolyte is an electrolyte for a solid oxide battery. Preferably, the electrolyte includes one or more of yttria-stabilized zirconia (YSZ), gadolinium-doped ceria (GDC), scandia-stabilized zirconia (ScSZ), samarium-doped ceria (SDC), and perovskite oxides, etc. Specifically, the perovskite oxides include BZY (BaZr 1-a Y a O 3-δ , 0 < a ≤ 0.5), BCY (BaCe 1-b Y b O 3-δ , 0 < b ≤ 0.5), and BZCY (BaZr 1-c-d Ce c Y d O 3-δ , 0.5 < c < 1, 0 < d ≤ 0.5), etc. More preferably, the electrolyte includes yttria-stabilized zirconia and / or gadolinium-doped ceria. These electrolytes can be the electrolytes for solid oxide batteries in the prior art.

[0037] In some embodiments, in step (1), the mass ratio of the nickel compound to the electrolyte is (10 - 80):(90 - 20), such as 10:90, 20:80, 30:70, 40:60, 50:50, 60:40, 70:30, or 80:20, etc.

[0038] In some embodiments, in step (1), the mixture comprising the nickel compound and the electrolyte may further comprise a pore-forming agent. The pore-forming agent may include, for example, starch. The amount of the pore-forming agent may be 1 to 15 parts by mass relative to the total amount of 100 parts by mass of the nickel compound and the electrolyte.

[0039] In some embodiments, in step (1), the mixture comprising the nickel compound and the electrolyte may further comprise a solvent. The solvent may comprise water and / or an organic solvent, such as an alcohol compound, specifically ethanol and / or isopropanol. The amount of solvent used may be 30 to 120 parts by mass relative to the total amount of 100 parts by mass of the nickel compound and the electrolyte.

[0040] In some embodiments, in step (1), the mixture comprising the nickel compound and the electrolyte can be prepared by mechanically mixing the nickel compound, the electrolyte, and other selectively included components (such as the pore-forming agent and / or solvent described above). The mechanical mixing may, for example, include ball milling. If the mixture contains a solvent, it may be dried after mixing and then molded.

[0041] In some embodiments, the molding process in step (1) may include pressing, etc.

[0042] In some embodiments, in step (2), the pre-firing temperature is 400~600°C, the pre-firing time is 1~3 hours, and the pre-firing is carried out in an oxidizing gas atmosphere. The oxidizing gas can be, for example, air. The pre-firing heating rate is preferably 2~5°C / min. After the pre-firing is completed, the temperature can be cooled to room temperature before subsequent high-temperature flash firing.

[0043] This invention, by controlling the pre-calcination temperature and time within the aforementioned range, enables the added pore-forming agents and other components to fully decompose, preventing defects such as electrode cracks caused by residual organic matter or sudden decomposition generating gas during subsequent high-temperature flash calcination. Furthermore, it allows for preliminary densification of the pre-calcined product, giving it suitable strength and preventing deformation or collapse during subsequent high-temperature flash calcination. Simultaneously, it establishes a preliminary interaction between nickel and the electrolyte, laying the foundation for subsequent electrode microstructure construction. If the pre-calcination temperature and time are below the aforementioned range, the above effects and benefits are difficult to fully realize. If the pre-calcination temperature and time are above the aforementioned range, it may lead to excessive sintering driving force between particles, causing excessive particle growth and agglomeration, resulting in uneven electrode grain size and poor microstructure.

[0044] In some embodiments, in step (2), the high-temperature flash burning time is 1~60s.

[0045] In some embodiments, in step (2), the high-temperature flash burning is achieved by Joule heating.

[0046] Specifically, the high-temperature flash burning includes: heating to 1500-3000℃ at a heating rate of 20-500℃ / s, maintaining the temperature at 1500-3000℃ for 1-60 seconds for high-temperature flash burning, and then cooling to room temperature at a cooling rate of 100-1000℃ / s. Preferably, the high-temperature flash burning temperature is 1500-1800℃, the time is 10-20 seconds, the heating rate is 100-200℃ / s, and the cooling rate is 200-800℃ / s.

[0047] More specifically, the high-temperature flash calcination includes the following process: placing the pre-calcined product in the middle of a carbon material, applying an electric current to the carbon material, controlling the heating rate at 20~500℃ / s (preferably 100~200℃ / s), heating to 1500~3000℃ (preferably 1500~1800℃) and holding for 1~60s (preferably 10~20s) for high-temperature flash calcination, then stopping the application of the current, and cooling to room temperature at a cooling rate of 100~1000℃ / s (preferably 200~800℃ / s) to obtain the product after high-temperature flash calcination. Applying the current to the carbon material is achieved by connecting electrodes to both ends of the carbon material. The carbon material is mainly used to conduct current to achieve Joule heating. The carbon material can be folded in half, and the pre-calcined product can be sandwiched in the middle of the carbon material, so that both the upper and lower surfaces of the pre-calcined product are in contact with the carbon material. Connecting external electrodes to both ends of the carbon material allows current to pass through and facilitates the uniformity of Joule heating. The applied current can be adjusted based on the heating rate described above, as long as the heating rate remains within the aforementioned range. The carbon material can be, for example, carbon fiber felt, carbon paper, or carbon cloth. The high-temperature flash calcination is preferably performed in a vacuum environment; performing it in an air atmosphere will affect the diffusion of Ni into the grains.

[0048] This invention employs Joule heating for high-temperature flash sintering, utilizing the rapid heating and cooling characteristics of Joule heating. By controlling the temperature, time, and heating / cooling rates within the aforementioned range, rapid sintering of nickel-based composite electrodes can be achieved. During rapid sintering, the material surface melts at high temperatures to form a liquid phase, promoting interparticle adhesion and enhancing the bonding force between particles. This also promotes particle growth and fusion, resulting in a more regular microstructure. Simultaneously, the inventors unexpectedly discovered that by employing high-temperature flash sintering and controlling its conditions within the aforementioned range, nickel atom activity is intensified. Nickel atoms can enter the electrolyte grains through vacancies, interstitials, and other defects in the electrolyte lattice, resulting in a higher nickel content (elemental doping) within the electrolyte grains of the electrode. In other words, rapid sintering during the high-temperature operation of this invention achieves Ni dispersion within the grains. Furthermore, because the high-temperature holding time and cooling time are both short, Ni precipitation and enrichment at grain boundaries are suppressed. If the temperature and time of high-temperature flash sintering are below the aforementioned range, sintering will be insufficient, and the aforementioned effects will be difficult to achieve. If the temperature and time of high-temperature flash burning exceed the above ranges, the microstructure of the material may be damaged, resulting in excessive stress that is difficult to eliminate even with subsequent low-temperature annealing. If the cooling rate of high-temperature flash burning is below the above ranges, Ni enrichment occurs at the grain boundaries, and the nickel content inside the grains is too low.

[0049] Furthermore, this invention places the pre-calcined product in the middle of a carbon material for high-temperature flash calcination. The carbon material has excellent electrical conductivity, ensuring uniform current flow throughout the system, allowing for uniform heating and guaranteeing the stability and uniformity of the flash calcination process. This contributes to obtaining electrodes with uniform performance. If carbon material is not used, and the two ends of the pre-calcined product are directly connected to the electrode, the current may not be able to flow uniformly onto the material, leading to structural and performance inhomogeneities in the electrode. Moreover, without the additional resistive heating provided by the carbon material, relying solely on the resistive heating between the electrode and the pre-calcined product may significantly slow down the heating rate, making rapid flash calcination difficult. This hinders the full effectiveness of suppressing nickel accumulation at grain boundaries and increasing the nickel content within the electrolyte grains.

[0050] In some embodiments, in step (2), the annealing temperature is 300~1400℃, preferably 300~1200℃, and more preferably 800~1200℃.

[0051] In some embodiments, in step (2), the annealing time is 0.5 to 20 hours, preferably 0.5 to 5 hours, and more preferably 1 to 3 hours.

[0052] In some embodiments, in step (2), the annealing heating rate is 2~5℃ / min, and the cooling rate is 2~5℃ / min. After cooling to room temperature, a nickel-based composite electrode is obtained.

[0053] In some embodiments, in step (2), the annealing is performed in an oxidizing gas atmosphere. The oxidizing gas may be, for example, air.

[0054] This invention employs low-temperature annealing after high-temperature flash firing. By controlling the temperature and time of low-temperature annealing within the aforementioned range, it can eliminate material stress, allowing atoms to rearrange and relax to a certain extent, reducing the risk of electrode cracking or deformation. Simultaneously, it can achieve more uniform grain size, further optimizing the electrode's microstructure. If the temperature and time of low-temperature annealing are below the aforementioned range, the effects of stress elimination and microstructure optimization are difficult to fully realize. If the temperature and time of low-temperature annealing are above the aforementioned range, it may lead to excessive grain growth, resulting in uneven grain size, and may also cause thermal damage and deformation to the electrode.

[0055] In some embodiments, the preparation method of the nickel-based composite electrode of the present invention specifically includes the following steps: Step 1, mixing and molding: The nickel compound and electrolyte are weighed according to a mass ratio of (10~80):(90~20), and then added to a ball mill jar. An appropriate amount of pore-forming agent and an appropriate amount of solvent are added. After adding the ball milling beads, the mixture is placed in a ball mill and ball-milled evenly. Then, it is poured out and dried to obtain a mixture powder containing the nickel compound and electrolyte. The mixture powder containing the nickel compound and electrolyte is then added to an agate grinding media and ground evenly. An appropriate amount of the mixture powder is weighed and placed in a tableting mold. After tableting under a pressure of 40~80MPa, a nickel-based composite electrode precursor is obtained. Step 2, pre-calcination: After the nickel-based composite electrode precursor is taken out from the tableting mold, it is placed in a heating furnace and heated to 400~600℃ in an air atmosphere at a heating rate of 2~5℃ / min. The product is pre-calcined at 600℃ for 1-3 hours, then cooled to room temperature in the furnace to obtain the pre-calcined product. Step 3: High-temperature flash calcination: The pre-calcined product is placed in the middle of a carbon material and placed in a heating furnace. Electrodes are connected to both ends of the carbon material. In a vacuum environment, current is applied to the carbon material, and the heating rate is controlled at 20-500℃ / s. The temperature is raised to 1500-3000℃ and held for 1-60 seconds for high-temperature flash calcination. Then the current is stopped, and the temperature is lowered to room temperature at a rate of 100-1000℃ / s to obtain the high-temperature flash calcined product. Step 4: Low-temperature annealing: The high-temperature flash calcined product is placed in a heating furnace and heated to 300-1400℃ in an air atmosphere at a heating rate of 2-5℃ / min. The temperature is held at 300-1400℃ for 0.5-20 hours for low-temperature annealing. Then the temperature is lowered to room temperature at a rate of 2-5℃ / min to obtain the nickel-based composite electrode.

[0056] This invention combines pre-sintering, high-temperature flash sintering, and low-temperature annealing, and by controlling these conditions within the aforementioned range, it suppresses nickel enrichment at the electrolyte grain boundaries in the electrode, thereby improving the ionic conductivity at the grain boundaries. Simultaneously, it allows for a higher nickel content within the electrolyte grains (especially those using YSZ as the electrolyte), exhibiting characteristics of a mixed-ion conductor; it also ensures uniform grain size, improving the electrode's microstructure; and it reduces the risk of electrode cracking or deformation. Furthermore, most existing sintering methods require long sintering times (10-40 hours) at 1400-1800℃, resulting in high energy consumption. Compared to existing sintering methods, this invention offers advantages such as simple process, short sintering time, high efficiency, and reduced energy consumption, achieving energy-saving effects.

[0057] According to a specific embodiment of the second aspect of the present invention, the present invention provides a nickel-based composite electrode, which is prepared by the above-described method for preparing a nickel-based composite electrode.

[0058] In some embodiments, the difference between the Ni content at the grain boundaries and the Ni content in the grains of the electrolyte in the nickel-based composite electrode is less than 6%.

[0059] In some embodiments, the Ni content in the electrolyte grains of the nickel-based composite electrode is 1-15%, preferably 2-14%.

[0060] This invention can suppress nickel enrichment at grain boundaries in the electrode, thereby significantly improving the ionic conductivity at the grain boundaries. Simultaneously, the electrolyte grains in the nickel-based composite electrode of this invention can have a high nickel content, resulting in a significant increase in both ionic and electronic conductivity, exhibiting characteristics of a mixed ionic conductor. Therefore, the nickel-based composite electrode of this invention possesses improved conductivity and overall performance.

[0061] The technical solutions of the present invention are specifically illustrated below through embodiments, but the present invention is not limited to these embodiments. Of course, various modifications can be made within the scope of the key points of the present invention.

[0062] Test Method: Nickel enrichment at the grain boundaries of the electrolyte in nickel-based composite electrodes: Using a FEI Titan G2 60–300 microscopy at 300 kV, STEM-HAADF (scanning transmission electron microscopy-high angle annular dark field) images and EDS-mapping (energy dispersive spectroscopy-mapping) images of the electrode samples were obtained. The presence of nickel enrichment at the grain boundaries of the electrolyte in the electrode was analyzed by observing the STEM-HAADF and EDS-mapping images.

[0063] The difference between the Ni content at the grain boundaries and the Ni content in the grains of the electrolyte in the nickel-based composite electrode: Using the aforementioned instruments and testing conditions, an EDS-mapping diagram was obtained. The Ni content at the grain boundaries and the Ni content in the grains were determined using the EDS-mapping diagram and the instrument's built-in software. The difference was then obtained by subtracting the two. The Ni content was calculated based on the total atomic weight of all metallic elements as 100%.

[0064] Ni content in the electrolyte grains of the nickel-based composite electrode: EDS-mapping diagrams were obtained using the instruments and testing conditions described above. The Ni content in the grains was determined using the EDS-mapping diagrams and the instrument's built-in software. The Ni content was calculated based on the total atomic weight of all metal elements as 100%.

[0065] Example 1

[0066] Step 1: Mixing and Shaping: Weigh NiO and YSZ at a mass ratio of 20:80, then add them to a ball mill jar. Add starch and anhydrous ethanol. The amount of starch added is 10 parts and the amount of anhydrous ethanol is 100 parts per 100 parts by mass of NiO and YSZ. After adding grinding beads, place the mixture in a ball mill and grind it evenly. Then pour it out and dry it to obtain a powder mixture containing nickel compounds and electrolytes. Then add the powder mixture containing nickel compounds and electrolytes to an agate grinding ball and grind it evenly. First, weigh an appropriate amount of the mixed powder and place it in a tableting mold. After tableting at 80 MPa, a nickel-based composite electrode precursor is obtained. Second, pre-calcination: After removing the nickel-based composite electrode precursor from the tableting mold, place it in a heating furnace and heat it to 500°C in air at a heating rate of 2°C / min. Maintain this temperature at 500°C for 2 hours for pre-calcination, then cool it to room temperature with the furnace to obtain the pre-calcined product. Third, high-temperature flash calcination: Fold the carbon fiber felt in half and place the pre-calcined product in the middle of the carbon fiber felt. The carbon fiber felt was placed in a heating furnace, and electrodes were connected to both ends. In a vacuum environment, an electric current was applied to the carbon fiber felt, controlling the heating rate at 200℃ / s. The temperature was raised to 1700℃ and held for 15 seconds for high-temperature flash calcination. Then, the applied current was stopped, and the temperature was lowered to room temperature at a rate of 800℃ / s to obtain the product after high-temperature flash calcination, denoted as 20N-YSZ-UHS. Step four: Low-temperature annealing: The product after high-temperature flash calcination was placed in a heating furnace and heated to 800℃ in an air atmosphere at a heating rate of 5℃ / min. The product is annealed at 800℃ for 2 hours, and then cooled to room temperature at a rate of 5℃ / min to obtain a nickel-based composite electrode, denoted as 20N-YSZ-UHS-800; or, the product after high-temperature flash calcination is placed in a heating furnace and heated to 1200℃ in air at a heating rate of 5℃ / min, annealed at 1200℃ for 2 hours, and then cooled to room temperature at a cooling rate of 5℃ / min to obtain a nickel-based composite electrode, denoted as 20N-YSZ-UHS-1200.

[0067] Figure 1 shows the STEM-HAADF and EDS-mapping images of the grains and grain boundaries of the two nickel-based composite electrodes prepared in this embodiment. Figure 1a shows the STEM-HAADF and EDS-mapping images of 20N-YSZ-UHS-800, and Figure 1b shows the STEM-HAADF and EDS-mapping images of 20N-YSZ-UHS-1200. As can be seen from Figure 1, there is no Ni enrichment at the YSZ grain boundaries of both 20N-YSZ-UHS-800 and 20N-YSZ-UHS-1200.

[0068] In this embodiment, the Ni content at the grain boundaries of the electrolyte in the 20N-YSZ-UHS-800 is 15.6%, and the Ni content in the grains is 13.7% (based on the total atomic weight of Ni, Y, and Zr being 100%), with a difference of 1.9%. In the 20N-YSZ-UHS-1200, the Ni content at the grain boundaries of the electrolyte is 14.3%, and the Ni content in the grains is 9.1% (based on the total atomic weight of Ni, Y, and Zr being 100%), with a difference of 5.2%. Therefore, this embodiment can eliminate Ni enrichment at the YSZ grain boundaries in the electrode, thereby improving the ionic conductivity at the grain boundaries. Furthermore, the electrolyte grains in the nickel-based composite electrode of this embodiment have a high nickel content, resulting in significantly increased ionic and electronic conductivity, exhibiting characteristics of a mixed ionic conductor.

[0069] For comparison, Figure 2 shows the STEM-HAADF and EDS-mapping images of the YSZ grain boundaries of a commercially available SOFC anode support. It can be seen that the fuel electrode prepared using the existing sintering method exhibits significant Ni enrichment at the YSZ grain boundaries.

[0070] Example 2

[0071] Step 1: Mixing and Molding: Weigh NiO and GDC at a mass ratio of 20:80, then add them to a ball mill jar. Add starch and anhydrous ethanol, with 10 parts starch and 100 parts anhydrous ethanol added compared to 100 parts by mass of NiO and GDC. After adding grinding beads, place the mixture in a ball mill and grind it evenly. Then pour it out and dry it to obtain a powder mixture containing nickel compounds and electrolytes. Then add the powder mixture containing nickel compounds and electrolytes to an agate grinding media and grind it evenly. Weigh an appropriate amount of the powder mixture and place it in a tableting mold. After tableting at 80 MPa, obtain the nickel-based composite electrode precursor. Step 2: Pre-calcination: After removing the nickel-based composite electrode precursor from the tableting mold, place it in a heating furnace and heat it to 500℃ in an air atmosphere at a heating rate of 2℃ / min. Hold it at 500℃ for 2 hours for pre-calcination. Step 1: Fiber calcination, followed by furnace cooling to room temperature to obtain the pre-calcined product; Step 2: High-temperature flash calcination: Fold the carbon fiber felt in half and place the pre-calcined product in the middle of the carbon fiber felt. Place it in a heating furnace, connect the two ends of the carbon fiber felt to electrodes, apply current to the carbon fiber felt in a vacuum environment, control the heating rate to be 200℃ / s, heat to 1500℃ and hold for 15s for high-temperature flash calcination, then stop applying current and cool to room temperature at a cooling rate of 800℃ / s to obtain the high-temperature flash calcined product, denoted as 20N-GDC-UHS; Step 3: Low-temperature annealing: Place the high-temperature flash calcined product in a heating furnace, heat to 800℃ in an air atmosphere at a heating rate of 5℃ / min, hold at 800℃ for 2h for low-temperature annealing, and then cool to room temperature at a cooling rate of 5℃ / min to obtain the nickel-based composite electrode, denoted as 20N-GDC-UHS-800.

[0072] Figure 4a shows the STEM-HAADF and EDS-mapping images of the grains and grain boundaries of the nickel-based composite electrode prepared in this embodiment. As can be seen from Figure 4a, there is no Ni enrichment at the GDC grain boundaries of 20N-GDC-UHS-800.

[0073] In this embodiment of the 20N-GDC-UHS-800, the Ni content at the grain boundaries of the electrolyte is 1.1%, and the Ni content in the grains is 2.3% (based on the total atomic weight of Ni, Gd, and Ce being 100%), with a difference of 1.2%. Therefore, the Ni content at the electrolyte grain boundaries in the nickel-based composite electrode of this embodiment is reduced, eliminating Ni enrichment at the GDC grain boundaries in the electrode and improving ionic conductivity.

[0074] Example 3

[0075] This embodiment is basically the same as Embodiment 1, except that: Step 3, high-temperature flash calcination: Fold the carbon fiber felt in half and place the pre-calcined product in the middle of the carbon fiber felt. Place it in a heating furnace, connect the two ends of the carbon fiber felt to electrodes, and apply current to the carbon fiber felt in a vacuum environment. Control the heating rate to 300℃ / s, raise the temperature to 2000℃ and hold for 2s for high-temperature flash calcination, then stop applying the current and cool it to room temperature at a cooling rate of 800℃ / s to obtain the product after high-temperature flash calcination. The remaining steps are the same as in Embodiment 1, except that the low-temperature annealing temperature is 800℃.

[0076] Figure 5a shows the STEM-HAADF and EDS-mapping images of the grains and grain boundaries of the nickel-based composite electrode in this embodiment. In this embodiment, the Ni content at the grain boundaries of the electrolyte in the nickel-based composite electrode is 15.7%, and the Ni content in the grains is 13.2% (based on the total atomic weight of Ni, Y, and Zr being 100%), a difference of 2.5%. There is no Ni enrichment at the YSZ grain boundaries of the nickel-based composite electrode in this embodiment. Furthermore, the electrolyte grains in this embodiment have a high nickel content.

[0077] Example 4

[0078] This embodiment is basically the same as Embodiment 1, except that: Step 3, high-temperature flash calcination: Fold the carbon fiber felt in half and place the pre-calcined product in the middle of the carbon fiber felt. Place it in a heating furnace, connect the two ends of the carbon fiber felt to electrodes, and apply current to the carbon fiber felt in a vacuum environment. Control the heating rate to be 20℃ / s, raise the temperature to 1500℃ and hold for 15s for high-temperature flash calcination. Then stop applying the current and cool down to room temperature at a cooling rate of 300℃ / s to obtain the product after high-temperature flash calcination. The remaining steps are the same as in Embodiment 1, except that the low-temperature annealing temperature is 1200℃.

[0079] Figure 6a shows the STEM-HAADF and EDS-mapping images of the grains and grain boundaries of the nickel-based composite electrode in this embodiment. In this embodiment, the Ni content at the grain boundaries of the electrolyte in the nickel-based composite electrode is 15.1%, and the Ni content in the grains is 12.8% (based on the total atomic weight of Ni, Y, and Zr being 100%), a difference of 2.3%. There is no Ni enrichment at the YSZ grain boundaries of the nickel-based composite electrode in this embodiment. Furthermore, the electrolyte grains in this embodiment have a high nickel content.

[0080] Comparative Example 1

[0081] This comparative example is basically the same as Example 1, except that: the carbon fiber felt is folded in half, and the pre-calcined product is placed in the middle of the carbon fiber felt. It is then placed in a heating furnace, and electrodes are connected to both ends of the carbon fiber felt. In an air atmosphere, an electric current is applied to the carbon fiber felt, controlling the heating rate at 200°C / s. The temperature is raised to 1500°C and held for 15 seconds for high-temperature flash calcination. Then, the current is stopped, and the temperature is lowered to room temperature at a rate of 800°C / s to obtain the product after high-temperature flash calcination. The remaining steps are the same as in Example 1, except that the low-temperature annealing temperature is 1200°C.

[0082] Figure 7a shows the STEM-HAADF and EDS-mapping images of the nickel-based composite electrode in this comparative example at the grain boundaries and the grain size. In this comparative example, the Ni content at the grain boundaries of the electrolyte in the nickel-based composite electrode is 9.5%, while the Ni content in the grains is 1.4% (based on the total atomic weight of Ni, Y, and Zr being 100%), a difference of 8.1%. It can be seen that the use of an air atmosphere during the flash calcination process in this comparative example affects the diffusion of Ni into the grains.

[0083] Comparative Example 2

[0084] This comparative example is basically the same as Example 1, except for the following step: High-temperature flash calcination: Fold the carbon fiber felt in half and place the pre-calcined product in the middle of the carbon fiber felt. Place it in a heating furnace, connect electrodes to both ends of the carbon fiber felt, and apply current to the carbon fiber felt in a vacuum environment. Control the heating rate at 300℃ / s, raise the temperature to 1500℃ and hold for 15s for high-temperature flash calcination. Then stop applying the current and cool it to room temperature at a rate of 5℃ / s to obtain the product after high-temperature flash calcination. The remaining steps are the same as in Example 1, except that the low-temperature annealing temperature is 1200℃.

[0085] Figure 8a shows the STEM-HAADF and EDS-mapping images of the nickel-based composite electrode in this comparative example at the grain boundaries and the crystallite. The Ni content at the grain boundaries of the electrolyte in this comparative example's nickel-based composite electrode is 15.3%, while the Ni content in the grains is 2.1% (based on the total atomic weight of Ni, Y, and Zr being 100%), a difference of 13.2%. It can be seen that the comparative example used an excessively low cooling rate, resulting in an excessively long cooling time. This led to Ni enrichment at the YSZ grain boundaries of the nickel-based composite electrode in this comparative example, and also resulted in an excessively low nickel content within the electrolyte grains.

[0086] Comparative Example 3

[0087] This comparative example prepared 20% NiO-doped YSZ using a conventional sintering method, including the following steps: Step 1, mixing and shaping: NiO and YSZ were weighed at a mass ratio of 20:80, then added to a ball mill jar, along with starch and anhydrous ethanol. The amount of starch added was 10 parts and the amount of anhydrous ethanol added was 100 parts per 100 parts by mass of NiO and YSZ. After adding grinding beads, the mixture was placed in a ball mill and ball-milled until homogeneous. The mixture was then poured out and dried to obtain a powder mixture containing nickel compounds and electrolytes. This powder mixture was then added to an agate grinding media and ground until homogeneous. An appropriate amount of the mixture was then weighed... The composite powder was placed in a tableting mold and tableted at 80 MPa to obtain a nickel-based composite electrode precursor. Step 2: Pre-firing, sintering and annealing: After the nickel-based composite electrode precursor was removed from the tableting mold, it was placed in a heating furnace and heated to 500°C in air at a heating rate of 2°C / min. It was then held at 500°C for 2 hours for pre-firing, then heated to 1400°C at a heating rate of 3°C / min and held at 1400°C for 10 hours. After that, it was cooled to 300°C at a cooling rate of 3°C / min and held at 300°C for 2 hours for low-temperature annealing. Finally, it was cooled to room temperature in the furnace to obtain a nickel-based composite electrode, denoted as 20N-YSZ.

[0088] In this comparative example, the Ni content at the grain boundaries of the electrolyte in the nickel-based composite electrode is 9.6%, while the Ni content in the grains is 1.2% (based on the total atomic weight of Ni, Y, and Zr being 100%), with a difference of 8.4%. It can be seen that Ni enrichment exists at the YSZ grain boundaries in this comparative example's nickel-based composite electrode, and the nickel content inside the electrolyte grains is too low.

[0089] Comparative Example 4

[0090] This comparative example prepared 20% NiO-doped GDC using a conventional sintering method, including the following steps: Step 1, Mixing and Shaping: NiO and GDC were weighed at a mass ratio of 20:80, then added to a ball mill jar, along with starch and anhydrous ethanol. The amount of starch added was 10 parts and the amount of anhydrous ethanol added was 100 parts per 100 parts by mass of NiO and GDC. After adding grinding beads, the mixture was ball-milled until homogeneous, then poured out and dried to obtain a powder mixture containing nickel compounds and electrolytes. This powder mixture was then added to an agate grinding media and ground until homogeneous. An appropriate amount of the mixture was then weighed... The composite powder was placed in a tableting mold and tableted at 80 MPa to obtain a nickel-based composite electrode precursor. Step 2: Pre-firing, sintering and annealing: After the nickel-based composite electrode precursor was removed from the tableting mold, it was placed in a heating furnace and heated to 500°C in air at a heating rate of 2°C / min. It was then held at 500°C for 2 hours for pre-firing, then heated to 1400°C at a heating rate of 3°C / min and held at 1400°C for 10 hours. After that, it was cooled to 300°C at a cooling rate of 3°C / min and held at 300°C for 2 hours for low-temperature annealing. Finally, it was cooled to room temperature in the furnace to obtain a nickel-based composite electrode, denoted as 20N-GDC.

[0091] In this comparative example, the Ni content at the grain boundaries of the electrolyte in the nickel-based composite electrode is 5.3%, while the Ni content in the grains is 1.1% (based on the total atomic weight of Ni, Gd, and Ce being 100%), with a difference of 4.2%. It can be seen that Ni enrichment exists at the GDC grain boundaries in this comparative example's nickel-based composite electrode, and the nickel content inside the electrolyte grains is too low.

[0092] Test case

[0093] The nickel-based composite electrodes prepared in the above examples and comparative examples were subjected to electrochemical impedance spectroscopy (EIS) testing. The testing procedure included using a Gamry electrochemical workstation with a frequency of 0.01 Hz to 100,000 Hz.

[0094] Figure 3 shows the electrochemical impedance spectroscopy (EIS) spectra of 20N-YSZ from Comparative Example 3 and 20N-YSZ-UHS-800 and 20N-YSZ-UHS-1200 from Example 1, tested at 200℃ (Figure 3a) and 800℃ (Figure 3b), respectively. As can be seen from Figure 3, the resistivity of the YSZ grain boundaries in the nickel-based composite electrode of Example 1 decreases while the conductivity increases. This demonstrates that eliminating the enrichment of Ni element at the YSZ grain boundaries in the nickel-based composite electrode can significantly improve the conductivity of the grain boundaries.

[0095] Figure 4b and c show the electrochemical impedance spectra of the 20N-GDC in Comparative Example 4 and the 20N-GDC-UHS-800 in Example 2, obtained under conditions of 200℃ (Figure 4b) and 800℃ (Figure 4c), respectively. As can be seen from Figure 4, the resistance of the GDC grain boundaries in the nickel-based composite electrode of Example 2 is reduced, while the conductivity is increased.

[0096] Therefore, no Ni enrichment was found at the YSZ and GDC grain boundaries in the nickel-based composite electrode prepared by the method of this embodiment (Figure 1 and Figure 4a). Comparing the electrochemical impedance spectroscopy results of the nickel-based composite electrode of this embodiment with those of the nickel-based composite electrode prepared by conventional sintering methods, it can be found that the conductivity of the YSZ and GDC grain boundaries is significantly improved (Figure 3 and Figure 4b and c).

[0097] Figure 5b shows the electrochemical impedance spectroscopy (EIS) of the nickel-based composite electrode of Example 3 at 250°C. It can be seen that the ultra-high temperature, short-time rapid sintering results in a lower ionic resistance. Figure 6b shows the EIS of the nickel-based composite electrode of Example 4 at 250°C. It can be seen that reducing the heating rate does not affect the ionic resistance of rapid sintering, which remains lower than that of conventional sintering. Figure 7b shows the EIS of the nickel-based composite electrode of Comparative Example 1 at 250°C. It can be seen that the air atmosphere affects the ionic resistance of rapid sintering, which is lower than that of conventional sintering. Figure 8b shows the EIS of the nickel-based composite electrode of Comparative Example 2 at 250°C. It can be seen that an excessively low cooling rate affects the ionic resistance of rapid sintering, which is close to that of conventional sintering.

[0098] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a nickel-based composite electrode, comprising the following steps: (1) A mixture containing nickel compound and electrolyte is shaped to obtain a nickel-based composite electrode precursor; (2) The nickel-based composite electrode precursor is pre-calcined, then flash-calcined at 1500~3000℃, and then annealed to obtain the nickel-based composite electrode.

2. The method for preparing the nickel-based composite electrode according to claim 1, wherein, In step (1), the nickel compound includes nickel oxide.

3. The method for preparing the nickel-based composite electrode according to claim 1, wherein, In step (1), the electrolyte is an electrolyte for solid oxide batteries; preferably, the electrolyte includes one or more of yttrium-stabilized zirconium oxide, gadolinium-doped cerium oxide, scandium-stabilized zirconium oxide, samarium-doped cerium oxide, and perovskite oxide; more preferably, the electrolyte includes yttrium-stabilized zirconium oxide and / or gadolinium-doped cerium oxide.

4. The method for preparing the nickel-based composite electrode according to claim 1, wherein, In step (1), the mass ratio of the nickel compound to the electrolyte is (10~80):(90~20).

5. The method for preparing the nickel-based composite electrode according to claim 1, wherein, In step (2), the pre-firing temperature is 400~600℃, the pre-firing time is 1~3h, and the pre-firing is carried out in an oxidizing gas atmosphere.

6. The method for preparing the nickel-based composite electrode according to claim 1, wherein, In step (2), the high-temperature flash burning time is 1~60s; preferably, in step (2), the high-temperature flash burning is achieved by Joule heating; preferably, in step (2), the high-temperature flash burning includes: heating to 1500~3000℃ at a heating rate of 20~500℃ / s, holding at 1500~3000℃ for 1~60s for high-temperature flash burning, and then cooling to room temperature at a cooling rate of 100~1000℃ / s; more preferably, the high-temperature flash burning includes the following process: placing the pre-burned product in the middle of the carbon material, applying current to the carbon material, controlling the heating rate to be 20~500℃ / s, heating to 1500~3000℃ and holding for 1~60s for high-temperature flash burning, then stopping the application of current, and cooling to room temperature at a cooling rate of 100~1000℃ / s to obtain the product after high-temperature flash burning.

7. The method for preparing the nickel-based composite electrode according to claim 1, wherein, In step (2), the annealing temperature is 300~1400℃, the annealing time is 0.5~20h, and the annealing is carried out in an oxidizing gas atmosphere.

8. A nickel-based composite electrode, which is prepared by the method of preparing a nickel-based composite electrode according to any one of claims 1-7.

9. The nickel-based composite electrode according to claim 8, wherein, The difference between the Ni content at the grain boundaries and the Ni content in the grains of the electrolyte in the nickel-based composite electrode is less than 6%.

10. The nickel-based composite electrode according to claim 8, wherein, The Ni content in the electrolyte grains of the nickel-based composite electrode is 1-15%.

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