A YSZ electrolyte and a method of making the same and a sofc cell

Abstract

The application discloses a kind of YSZ electrolyte and preparation method and SOFC cell, it is related to battery field, comprising: zirconium salt, yttrium salt and doping salt are dissolved in mixed solvent, obtain precursor solution, wherein, doping salt is selected from lithium nitrate, sodium nitrate, potassium nitrate or rubidium nitrate, mixed solvent includes N, N-dimethylformamide, ethanol and deionized water;Precursor solution is heated under stirring condition, make precursor solution crystallization, obtain solid precursor;Solid precursor is carried out first heat treatment, and make solid precursor powderization;Powderized solid precursor is carried out second heat treatment in air atmosphere, and the product of second heat treatment is ground, obtain YSZ electrolyte powder;YSZ electrolyte powder is sequentially carried out forming and sintering, obtain YSZ electrolyte, wherein, YSZ electrolyte is 8YSZ electrolyte modified by metal element contained in doping salt.The application can improve the mixing uniformity of zirconium component, yttrium component and metal modified component.

Description

Technical Field

[0001] This invention relates to the field of batteries, specifically to a YSZ electrolyte, its preparation method, and an SOFC battery. Background Technology

[0002] Solid oxide fuel cells (SOFCs) are power generation devices that directly convert the chemical energy of fuel into electrical energy. The electrolyte layer is a key component for conducting oxygen ions and isolating fuel gases from oxidizing gases. Yttrium-stabilized zirconia (YSZ) possesses good chemical stability, mechanical strength, and oxygen ion conductivity, and is often used as an electrolyte material for SOFCs. Among them, 8YSZ, containing 8 mol% Y₂O₃, is a commonly used material in YSZ electrolytes. However, it typically requires a high sintering temperature to obtain a dense structure that meets the application requirements. Furthermore, its oxygen ion conductivity decreases as the operating temperature decreases. Therefore, reducing the sintering densification temperature of 8YSZ electrolytes and improving its oxygen ion conductivity is an important research direction in this field.

[0003] Existing technologies typically modify YSZ electrolytes by adding lithium salts. For example, YSZ powder is mixed with lithium salts through mechanical grinding, followed by molding and sintering; or, during battery operation, the molten lithium salt component is infiltrated along the electrolyte grain boundaries to improve the electrolyte's sintering performance or ion conductivity. While these methods can introduce monovalent metal components into YSZ electrolytes, the distribution of these components within the YSZ material still requires further improvement.

[0004] Therefore, existing technologies still suffer from insufficient uniformity in the mixing of zirconium, yttrium, and monovalent metal modification components, making it difficult to obtain 8YSZ electrolytes with uniform monovalent metal element modification. How to improve the mixing uniformity of these components to prepare 8YSZ electrolytes modified with monovalent metal elements is a technical problem that needs to be solved in this field. Summary of the Invention

[0005] This invention aims to address, to a certain extent, one of the technical problems in related technologies. To this end, this invention provides a YSZ electrolyte, its preparation method, and an SOFC battery, which can improve the mixing uniformity of zirconium, yttrium, and monovalent metal modified components, and obtain a monovalent metal modified 8YSZ electrolyte.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a YSZ electrolyte, comprising: Zirconium salt, yttrium salt, and dopant salt are dissolved together in a mixed solvent to obtain a precursor solution, wherein the dopant salt is selected from lithium nitrate, sodium nitrate, potassium nitrate, or rubidium nitrate, and the mixed solvent includes N,N-dimethylformamide, ethanol, and deionized water; The precursor solution is heated under stirring conditions to crystallize the precursor solution and obtain a solid precursor. The solid precursor is subjected to a first heat treatment to remove organic matter from the solid precursor and to pulverize the solid precursor; The powdered solid precursor is subjected to a second heat treatment in an air atmosphere, and the product of the second heat treatment is ground to obtain YSZ electrolyte powder. The YSZ electrolyte powder is sequentially shaped and sintered to obtain the YSZ electrolyte, wherein the YSZ electrolyte is an 8YSZ electrolyte modified by the metal elements contained in the doped salt.

[0007] In this application, zirconium salts, yttrium salts, and lithium nitrate, sodium nitrate, potassium nitrate, or rubidium nitrate are dissolved together in a mixed solvent composed of N,N-dimethylformamide, ethanol, and deionized water. This allows the metal components to be thoroughly mixed in the liquid phase before being heated and crystallized to retain this uniformly distributed state in the solid precursor. Subsequently, a first heat treatment removes organic matter and pulverizes the precursor, which improves heat and mass transfer conditions in subsequent processing. A second heat treatment in an air atmosphere further removes residual components and promotes the formation of modified YSZ powder. After grinding, shaping, and sintering, the corresponding monovalent metal element-modified 8YSZ electrolyte is obtained. Thus, this method can reduce local component segregation and powder agglomeration that are prone to occur in solid-phase mixing, and uniformly introduce lithium, sodium, potassium, or rubidium elements into the YSZ electrolyte system while maintaining the main crystalline phase of 8YSZ cubic fluorite. Furthermore, potassium and rubidium modification can also promote the sintering densification of electrolyte ceramic sheets. Among them, potassium-modified YSZ has a lower ohmic resistance, while rubidium-modified YSZ has a lower oxygen ion migration activation energy and a higher output voltage.

[0008] Optionally, the zirconium salt is zirconium acetate, and the yttrium salt is yttrium nitrate hexahydrate.

[0009] Optionally, the molar ratio of the doped salt to the total molar ratio of Y2O3 and ZrO2 in the 8YSZ is (3-8):100.

[0010] Optionally, the molar ratio of N,N-dimethylformamide, ethanol and deionized water in the mixed solvent is (1.0-2.0):(0.4-0.8):(0.3-0.7), and the total concentration of metal ions in the precursor solution is 0.05-0.2 mol / L.

[0011] Optionally, the mixture formed by the zirconium salt, the yttrium salt, the doped salt, and the mixed solvent is stirred at 40–70°C for 6–15 hours to obtain the precursor solution.

[0012] Optionally, the step of heating the precursor solution under stirring conditions includes: continuously stirring the precursor solution at 80–120°C until crystallization occurs, thereby obtaining the solid precursor.

[0013] Optionally, the temperature of the first heat treatment is 250–350°C; the temperature of the second heat treatment is 550–650°C, and the treatment time is 2–5 hours; the grinding time of the product after the second heat treatment is 20–60 minutes.

[0014] Optionally, the forming is dry pressing, and the pressure of the dry pressing is 15-30 MPa; the sintering temperature is 1300-1500℃, and the sintering time is 2-5 hours; the heating rate and cooling rate of the second heat treatment and the sintering are both 150-250℃ / h.

[0015] Furthermore, this invention also provides a YSZ electrolyte, which is prepared by the aforementioned preparation method. The reasoning process for the beneficial effects of the YSZ electrolyte provided by this invention is similar to that of the aforementioned preparation method, and will not be repeated here.

[0016] Furthermore, the present invention also provides an SOFC battery, comprising an anode, a cathode, and an electrolyte layer disposed between the anode and the cathode, the electrolyte layer being formed of the aforementioned YSZ electrolyte. The reasoning process for the beneficial effects of the SOFC battery provided by the present invention and the aforementioned YSZ electrolyte is similar, and will not be repeated here.

[0017] These features and advantages of the present invention will be disclosed in detail in the following specific embodiments and accompanying drawings. The preferred embodiments or means of the present invention will be shown in detail in conjunction with the accompanying drawings, but are not intended to limit the technical solutions of the present invention. In addition, each of these features, elements and components appearing in the following text and drawings is a plurality of, and different symbols or numbers are used for convenience of representation, but all represent parts with the same or similar construction or function. Attached Figure Description

[0018] The present invention will be further described below with reference to the accompanying drawings: Figure 1 The images show the sintered YSZ electrolyte ceramic sheets obtained in Examples 1-4 and Comparative Example 1. Figure 2 The X-ray diffraction patterns of the YSZ electrolyte ceramic sheets obtained in Examples 1-4 and Comparative Example 1 are shown below. Figure 3The X-ray photoelectron spectra of the YSZ electrolyte ceramic sheets obtained in Examples 1-4 and Comparative Example 1 are shown below. Figure 3 In the diagram, 'a' represents the energy spectrum of Y 3d5 / 2. Figure 3 In the diagram, b represents the energy spectrum of Zr 3d5 / 2. Figure 3 c in the spectrum is the O 1s energy spectrum. Figure 3 In the diagram, d represents the energy spectra of Li 1s, Na 1s, K 2p3 / 2, and Rb 3d5 / 2. Figure 4 This is a cross-sectional scanning electron microscope image of the unmodified YSZ electrolyte ceramic sheet obtained in Comparative Example 1. Figure 5 This is a cross-sectional scanning electron microscope image of the Li-YSZ electrolyte ceramic sheet obtained in Example 1; Figure 6 This is a cross-sectional scanning electron microscope image of the Na-YSZ electrolyte ceramic sheet obtained in Example 2; Figure 7 This is a cross-sectional scanning electron microscope image of the K-YSZ electrolyte ceramic sheet obtained in Example 3; Figure 8 This is a cross-sectional scanning electron microscope image of the Rb-YSZ electrolyte ceramic sheet obtained in Example 4; Figure 9 This is a scanning electron microscope image of the surface of the Li-YSZ electrolyte ceramic sheet obtained in Example 1; Figure 10 The Arrhenius fitting plots of the ohmic resistance of the YSZ electrolyte ceramic sheets obtained in Examples 1-4 and Comparative Example 1 are shown. Figure 11 The Nyquist spectra of the electrochemical impedance spectroscopy of solid oxide fuel cells assembled using the electrolyte ceramic sheets obtained in Examples 1, 3, and 4, respectively, at 800°C. Figure 12 The current-voltage characteristic curves of solid oxide fuel cells assembled using the electrolyte ceramic sheets obtained in Examples 1, 3, and 4 are shown at 800°C. Detailed Implementation

[0019] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described are intended to explain the present invention and should not be construed as limiting the invention.

[0020] The terms "an embodiment," "example," or "example" used in this specification refer to a particular feature, structure, or characteristic described in connection with the embodiment itself that may be included in at least one embodiment disclosed in this application. The phrase "in an embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment.

[0021] This invention provides a method for preparing a YSZ electrolyte. YSZ refers to yttrium-stabilized zirconium oxide, and the resulting YSZ electrolyte is specifically 8YSZ modified with potassium, rubidium, lithium, or sodium. The term 8YSZ here indicates the compositional relationship between ZrO2 and Y2O3 forming the yttrium-stabilized zirconium oxide matrix; that is, when calculated based solely on the total molar amount of ZrO2 and Y2O3, the molar percentage of ZrO2 is 92%, and the molar percentage of Y2O3 is 8%. Lithium nitrate, sodium nitrate, potassium nitrate, or rubidium nitrate are additional dopant salts added to the above 8YSZ composition. It is understood that the "8" in "8YSZ" does not indicate that Y2O3 accounts for 8% of all components, including potassium, rubidium, lithium, or sodium, in the final electrolyte, nor does it indicate that the final electrolyte consists only of ZrO2 and Y2O3. Rather, it is used to characterize the relative composition between ZrO2 and Y2O3 constituting the YSZ matrix.

[0022] This invention employs a liquid-phase precursor method, mixing the zirconium and yttrium components used to form 8YSZ with the dopant salt used for modification in a solution state. Compared to the direct mechanical mixing of pre-formed YSZ powder and dopant salt powder, in this invention, each metal component first exists in a dissolved state within the same liquid phase system, and then, with solvent removal, they jointly form a solid precursor. Therefore, the dopant component is not merely attached to the surface of the pre-formed YSZ particles, but is distributed co-located with the zirconium and yttrium components during the YSZ precursor formation stage. This helps reduce the possibility of dopant salt precipitating concentratedly at local grain boundaries or forming distinct independent salt phases.

[0023] In the preparation process, zirconium salt, yttrium salt, and dopant salt are first dissolved together in a mixed solvent to obtain a precursor solution. It should be noted that "co-dissolution" here means that the zirconium salt, yttrium salt, and dopant salt are all ultimately dissolved and coexist in the same mixed solvent system; it does not require that the three raw materials be added simultaneously. In practice, the mixed solvent can be prepared first, and then the zirconium salt, yttrium salt, and dopant salt can be added sequentially; alternatively, one or two salts can be dissolved first, and then the remaining raw materials can be added; or each salt can be partially dissolved in the mixed solvent before being combined. As long as there are no undissolved raw materials visible to the naked eye in the final system, and the zirconium component, yttrium component, and dopant component are in the same continuous liquid phase, co-dissolution can be considered complete.

[0024] Zirconium salts are used to provide a zirconium source for the formation of zirconium oxide, and yttrium salts are used to provide a yttrium source for stabilizing the crystal structure of zirconium oxide. The zirconium salt is a soluble zirconium salt capable of dissolving in a mixed solvent and undergoing a first heat treatment and a second heat treatment to form a zirconium oxide component; the yttrium salt is a soluble yttrium salt capable of dissolving in a mixed solvent and undergoing a first heat treatment and a second heat treatment to form a yttrium oxide component. Additionally, the zirconium salt may include one or more of zirconium acetate, zirconium oxynitrate, and zirconium nitrate; the yttrium salt may include one or more of yttrium nitrate and yttrium acetate.

[0025] In a preferred embodiment, the zirconium salt is zirconium acetate, and the yttrium salt is yttrium nitrate hexahydrate. Zirconium acetate can form a homogeneous liquid phase containing zirconium in the mixed solvent and can be converted into zirconium oxide-related components during subsequent heat treatment; yttrium nitrate hexahydrate can provide yttrium and can coexist with zirconium acetate in the precursor solution. By using zirconium and yttrium salts that are soluble in the same solvent system, the zirconium and yttrium components do not need to rely on mechanical contact between solid particles to achieve mixing, which is beneficial for forming a uniform zirconium and yttrium distribution at a smaller scale.

[0026] The amounts of zirconium and yttrium salts are determined according to the composition requirements of 8YSZ. When calculating the amounts of zirconium and yttrium salts, the amounts used to form ZrO2 and Y2O3 are determined based on the amount of zirconium and yttrium provided by the zirconium salts, respectively, ensuring a molar percentage composition of 92:8 for ZrO2 and Y2O3 formed from the zirconium and yttrium salts. This calculation is only used to determine the relative proportions of zirconium and yttrium components in the 8YSZ matrix and does not include potassium nitrate, rubidium nitrate, mixed solvents, or components volatilized or decomposed during heat treatment in the total molar amount of ZrO2 and Y2O3.

[0027] The doping salt is selected from lithium nitrate, sodium nitrate, potassium nitrate, or rubidium nitrate. When only potassium nitrate is used, a potassium-modified 8YSZ electrolyte is obtained; when only rubidium nitrate is used, a rubidium-modified 8YSZ electrolyte is obtained; when only lithium nitrate is used, a lithium-modified 8YSZ electrolyte is obtained; and when only sodium nitrate is used, a sodium-modified 8YSZ electrolyte is obtained. In other embodiments, the doping salt can also be selected from various nitrates. Using nitrates as the doping element source allows metal ions to dissolve into the precursor solution along with the nitrate and co-convert with the zirconium and yttrium components during subsequent crystallization and heat treatment.

[0028] The molar ratio of the dopant salt to the total molar ratio of Y₂O₃ and ZrO₂ in 8YSZ is (3–8):100. In this ratio, the denominator is the total amount of ZrO₂ and Y₂O₃ determined based on the amount of zirconium and yttrium salts added, excluding the amount of the dopant salt; the numerator is the actual amount of nitrate added. When only one dopant salt is added, the numerator is the molar amount of that dopant salt; when multiple nitrates are added simultaneously, the numerator is the sum of the molar amounts of the multiple nitrates. For example, when the total molar amount of ZrO₂ and Y₂O₃ is calculated as 100 parts, the total molar amount of the multiple nitrates is 3–8 parts.

[0029] Controlling the amount of dopant salt within the aforementioned range can avoid the adverse effects of excessively low or high doping levels. If the doping level is too low, the introduced metal element is insufficient, potentially having a negligible impact on the sintering process, lattice environment, and oxygen vacancy distribution of YSZ. If the doping level is too high, exceeding the range that the YSZ system can uniformly accommodate and disperse, it may increase the risk of dopant enrichment in localized areas or the formation of a second phase. Using a doping range of 3% to 8% can introduce sufficient modifying components while reducing the possibility of excessive doping disrupting the homogeneity of the YSZ bulk phase. This range can preferably be further controlled to 5% to 5.5%.

[0030] The mixed solvent comprises N,N-dimethylformamide, ethanol, and deionized water. These three solvents are not used separately in unrelated processes, but rather together to form a continuous liquid phase when preparing the precursor solution. Deionized water exhibits good solubility for lithium nitrate, sodium nitrate, potassium nitrate, and rubidium nitrate; N,N-dimethylformamide and ethanol, together with deionized water, regulate the solubility and volatility of the mixed solvent, ensuring a uniform distribution of different precursor salts within the same liquid phase. Using deionized water instead of ordinary water containing numerous impurity ions reduces the likelihood of foreign metal ions and inorganic anions being introduced into the precursor and final electrolyte.

[0031] The molar ratio of N,N-dimethylformamide, ethanol, and deionized water in the mixed solvent is (1.0–2.0):(0.4–0.8):(0.3–0.7). This molar ratio refers to the initial molar ratio of the three solvents added during the preparation of the mixed solvent, not the ratio of the residual solvents after heating and evaporation. The amounts of the three solvents can be converted into actual mass or volume based on their respective molar mass and purity before weighing. By controlling the three solvents within the above ratio range, the dissolution requirements of zirconium salts, yttrium salts, and doped salts can be met, and the precursor solution can be gradually concentrated and crystallized during subsequent heating. The preferred molar ratio of N,N-dimethylformamide, ethanol, and deionized water in the mixed solvent is 1.4:0.62:0.5.

[0032] The total concentration of metal ions in the precursor solution is 0.05–0.2 mol / L. Here, "total concentration of metal ions" refers to the ratio of the total amount of metal ions introduced by zirconium salts, yttrium salts, and dopant salts to the volume of the prepared precursor solution. When using only potassium nitrate, the metal ions include at least zirconium, yttrium, and potassium ions; when using only rubidium nitrate, the metal ions include at least zirconium, yttrium, and rubidium ions. This concentration is calculated as the sum of the amounts of each metal ion, excluding nitrate, acetate, and solvent molecules from the total amount of metal ions.

[0033] Controlling the total concentration of metal ions within the range of 0.05–0.2 mol / L ensures sufficient dissolution of the precursor salt in the mixed solvent while avoiding excessive dilution that would significantly prolong subsequent solvent removal time. If the precursor solution concentration is too low, more solvent is required for the same metal component, increasing the amount of solvent that needs to be removed during crystallization. Conversely, if the precursor solution concentration is too high, the salt may not dissolve sufficiently or may precipitate locally before formal heating for crystallization, thus weakening the effect of homogeneous mixing in the liquid phase. Therefore, the aforementioned concentration range is beneficial for balancing raw material dissolution, solution homogeneity, and subsequent crystallization efficiency. Preferably, the total concentration of metal ions can be 0.08–0.12 mol / L.

[0034] During the preparation of the precursor solution, the mixture of zirconium salt, yttrium salt, dopant salt, and mixed solvent is stirred at 40–70°C for 6–15 hours. The main purpose of this stage is to promote the dissolution of the raw materials and to ensure the uniform dispersion of the zirconium, yttrium, and dopant components in the liquid phase, rather than to induce significant crystallization of the precursor solution. In operation, the mixture can be heated to the set temperature before starting the stirring time; alternatively, the temperature can be gradually increased to the set temperature during stirring. The stirring equipment can be a magnetic stirrer or a mechanical stirrer, as long as it ensures continuous flow of the liquid in the container and prevents long-term sedimentation at the bottom.

[0035] Stirring at 40–70°C increases the dissolution rate of salts and reduces concentration differences between different locations in the precursor solution. At excessively low temperatures, the dissolution and diffusion of some raw materials are slow, requiring a longer time to obtain a homogeneous solution; at excessively high temperatures, the mixed solvent may evaporate rapidly before all raw materials are fully dissolved, leading to localized concentration of the solution. Therefore, controlling the temperature at 40–70°C and maintaining a stirring time of 6–15 hours allows sufficient time for the raw materials to dissolve and mix. After this step, the resulting precursor solution should be uniformly homogeneous, with no obvious stratification of raw materials or a large number of undissolved particles in the container.

[0036] After obtaining the precursor solution, it is further heated under stirring to crystallize and obtain a solid precursor. The heating temperature for this step is 80–120°C. "Crystallization" refers to the gradual evaporation of the mixed solvent, resulting in an increase in the salt concentration in the precursor solution, ultimately forming a solid crystalline precursor containing zirconium, yttrium, and dopant components. It is not required to form a single crystal with a specific shape or size, nor is it required to confirm through crystallographic methods that the obtained solid is a single crystal. Crystallization is considered complete when the precursor system gradually transforms from a free-flowing solution into a thick slurry, and further forms a solid material that is essentially free of visible free liquid.

[0037] Continuing to stir during crystallization keeps the precursor solution mixed during concentration, reducing the possibility of different salts precipitating separately in different areas of the container due to their varying solubilities. If the solvent is rapidly evaporated immediately after stirring stops, different local concentrations may form at the bottom of the container, near the liquid surface, and near the heating surface, causing the dopant salt to accumulate in localized areas. Continuous stirring ensures that the precipitating solid is in constant contact with the remaining liquid phase, which is beneficial for the zirconium, yttrium, and potassium or rubidium components to form a homogeneous solid precursor.

[0038] Maintaining the crystallization temperature between 80 and 120°C allows for the removal of the mixed solvent at an appropriate rate. Below this range, solvent removal is slower, prolonging the crystallization time; at excessively high temperatures, the solvent may volatilize violently, causing the precursor to rapidly crust over near the heated surface or form hard lumps that are difficult to stir further. In practice, the stirring speed can be appropriately reduced based on changes in material viscosity, but stirring should be maintained while the system still retains flowability. Once the precursor has solidified and effective stirring can no longer be maintained, stirring can be stopped, and the crystallization step can be terminated.

[0039] The resulting solid precursor is a mixed solid containing zirconium, yttrium, and doped metals, formed by the transformation of the liquid-phase precursor. In addition to the metal components, the solid precursor may also contain water of crystallization, bound water, residual solvent, acetate, nitrate, and other components that can volatilize or decompose during subsequent heat treatment. Therefore, the solid precursor cannot be directly equated to the final YSZ electrolyte powder and requires both a first heat treatment and a second heat treatment.

[0040] Subsequently, the solid precursor undergoes a first heat treatment to remove organic matter and pulverize it. The temperature of the first heat treatment is 250–350°C. The first heat treatment can be performed in an air environment using heating equipment such as a heating plate, oven, or air furnace. The type of equipment used for the first heat treatment is not a limitation of this invention, as long as it enables the solid precursor to reach the appropriate temperature as a whole and allows the volatile substances generated by heating to be discharged.

[0041] The first heat treatment primarily serves to remove organic components and loosen and pulverize the precursor. Under these temperature conditions, organic components introduced into the precursor, such as N,N-dimethylformamide, ethanol, and acetate, volatilize or decompose. The precursor, initially formed as lumps or agglomerates due to crystallization, gradually loses its binding effect from the organic phase, thus becoming loose and forming a powdery material. It should be noted that "pulverization" here does not require immediate attainment of fine powder with a strict particle size distribution after the first heat treatment. Rather, it refers to the transformation of the solid precursor from a relatively dense, lumpy substance formed by crystallization into a loose, powdery, or brittle agglomerated material that can be collected, crushed, or easily dispersed.

[0042] When the first heat treatment temperature is below 250℃, some organic components may not be fully volatilized or decomposed, leading to concentrated gas release or significant agglomeration during the subsequent second heat treatment. When the first heat treatment temperature is above 350℃, the precursor may undergo rapid inorganic transformation before the organic matter is uniformly discharged, which is not conducive to maintaining a loose powder state. Therefore, by performing the first heat treatment at 250–350℃, a significant amount of organic matter can be removed in advance and the precursor can be pulverized, providing a material with more uniform heat and mass transfer conditions for the subsequent second heat treatment in an air atmosphere.

[0043] The final state of the first heat treatment can be determined based on the material's state. The first heat treatment can be terminated when the solid precursor no longer exhibits significant wetness or agglomeration, the material transforms from a blocky state into a loose, breakable, or dispersible powder, and no significant volatile organic compounds are produced upon continued heating. Obtaining the final crystal structure is not a necessary condition for the first heat treatment to end; its focus is on organic matter removal and pulverization. The further formation and stabilization of the final YSZ-related phases are mainly achieved through subsequent second heat treatment and sintering.

[0044] After the first heat treatment, the powdered solid precursor undergoes a second heat treatment in an air atmosphere. An air atmosphere refers to a heat treatment space that is connected to or vented with air, allowing the material to be heated in an oxygen-containing environment. An air atmosphere does not require the use of high-purity oxygen, nor does it require additional adjustment of the oxygen content in the air. Using an air atmosphere facilitates further oxidation and removal of any organic components that may remain after the first heat treatment, and promotes the conversion of zirconium, yttrium, and potassium and / or rubidium components into oxide electrolyte powders.

[0045] The second heat treatment is performed at a temperature of 550–650℃ for 2–5 hours. The second heat treatment temperature is higher than the first heat treatment temperature. Its main function is no longer merely to remove organic matter, but to further react and transform the inorganic components in the powdered precursor, forming potassium and / or rubidium-modified YSZ electrolyte powder. Since the zirconium salt, yttrium salt, and doped salt have already dissolved together in the same liquid phase before forming the solid precursor, the distribution distance between the components is relatively small. Therefore, mixing during the second heat treatment does not require complete reliance on long-distance diffusion between different solid particles.

[0046] When the second heat treatment temperature is below 550℃, some components in the precursor may not be fully converted, resulting in insufficient composition and phase stability of the powder. When the treatment temperature is above 650℃, the powder may exhibit significant particle growth or hard agglomeration, increasing the difficulty of subsequent grinding. Therefore, controlling the second heat treatment temperature at 550–650℃ and maintaining it for 2–5 hours can ensure sufficient thermal conversion of the precursor while preventing excessive sintering of the powder before it enters the molding process.

[0047] The heating and cooling rates for the second heat treatment are both 150–250 °C / h. The heating rate refers to the average rate of temperature change as the material rises from a lower temperature to the target temperature of the second heat treatment, and the cooling rate refers to the average rate of temperature change as the material decreases from the second heat treatment temperature to the lower temperature. Both are controlled within the above range; this does not mean that the heating and cooling rates must be different values, nor does it mean they correspond to two different fixed endpoints. In actual operation, the heating and cooling rates can be the same, or different values ​​within the range of 150–250 °C / h can be selected respectively.

[0048] By controlling the heating rate, the concentrated decomposition and rapid gas release of residual components inside the powder can be avoided in a short period of time, thereby reducing the possibility of powder splashing or local agglomeration. By controlling the cooling rate, the temperature gradient between different locations of the material can be reduced, thus lowering the risk of thermal stress caused by rapid cooling. Preferably, the heating rate and cooling rate of the second heat treatment are both 200℃ / h.

[0049] After the second heat treatment, the product is ground. During heating, the product may form soft agglomerates, which need to be broken up by grinding to improve powder uniformity. The grinding time is 20–60 minutes, preferably 30 minutes. Grinding can be done using a mortar and pestle, or other grinding equipment suitable for ceramic powder processing that will not introduce impurities affecting electrolyte performance. The grinding equipment and grinding media should be kept clean to prevent large amounts of iron, silicon, or other foreign elements from entering the powder.

[0050] The purpose of grinding is not to change the chemical composition of the YSZ electrolyte, but to form a uniform powder suitable for subsequent molding from the second heat treatment product. If the grinding time is too short, the agglomerates formed during the second heat treatment may not be sufficiently broken up, resulting in uneven particle accumulation inside the blank during dry pressing. If the grinding time is too long, it will increase the processing time and may introduce impurities due to wear of the grinding media. Therefore, controlling the grinding time between 20 and 60 minutes can achieve a balance between breaking up agglomerates and controlling processing costs.

[0051] After grinding, metal element-modified YSZ electrolyte powder is obtained. Here, "modification" refers to the introduction of metal elements through the aforementioned four nitrates, followed by co-dissolution, co-crystallization, and heat treatment processes, resulting in their distribution within the YSZ system. "Modification" does not require the metal elements introduced into the final electrolyte to occupy a specific lattice position, nor does it require maintaining a specific lattice occupancy pattern.

[0052] Subsequently, the YSZ electrolyte powder is sequentially shaped and sintered. "Sequentially" here means that the loose powder is first formed into a green body with a predetermined shape, and then the green body is sintered at high temperature. Shaping and sintering are two different processes, and the second heat treatment should not be equated with the final sintering. The second heat treatment targets the powdered solid precursor, and its temperature is 550–650℃; the final sintering targets the shaped green body, and its temperature is 1300–1500℃. The former is mainly used to form and stabilize the electrolyte powder, while the latter is mainly used to densify the shaped green body and form a ceramic body that can be used as an electrolyte layer.

[0053] Dry pressing is the preferred molding process. During dry pressing, the ground YSZ electrolyte powder is added to a molding die, and pressure is applied to the powder using a tablet press or other pressure equipment. The pressure during dry pressing is 15–30 MPa. The die can be circular, rectangular, or other shapes depending on the final application shape of the electrolyte, and the resulting blank can be a disc, a flat plate, or a sheet-like body adapted to the battery structure. It should be noted that "molding" does not limit the final product to a disc, nor does it limit the fixed diameter and thickness, as long as the powder can be pressed into a blank with a certain shape stability and suitable for subsequent sintering. Alternatively, isostatic pressing and other molding processes can also be used.

[0054] When the dry pressing pressure is below 15 MPa, the contact between powder particles is insufficient, resulting in low strength of the green body and making it prone to corner chipping, cracking, or pulverization during demolding or transfer. When the dry pressing pressure is above 30 MPa, large density gradients may form at different locations of the green body due to differences in stress and friction, leading to uneven stress during sintering shrinkage. Therefore, dry pressing at 15–30 MPa can ensure that the green body has appropriate initial density and handling strength, while reducing internal stress unevenness caused by excessive pressure. Preferably, the dry pressing pressure is 20 MPa.

[0055] After forming, the green body is sintered. The sintering temperature is 1300–1500℃, and the sintering time is 2–5 hours. During sintering, adjacent particles in the green body diffuse and migrate, sintering necks form and grow at particle contact points, and the pores between powder particles gradually shrink, causing the green body to shrink and form a YSZ electrolyte ceramic body with high density. The sintered electrolyte needs to have a continuous solid structure to separate the anode and cathode atmospheres in the solid oxide fuel cell while providing an oxygen ion conduction pathway.

[0056] The introduction of potassium, rubidium, lithium, or sodium can all affect the sintering process of YSZ. Appropriate amounts of alkali metal components can promote particle rearrangement and mass migration during high-temperature processes, thereby facilitating the elimination of interparticle porosity and densification of the green body. This effect stems from the fact that the aforementioned four doping elements, together with the 8YSZ powder, undergo precursor formation and heat treatment, resulting in a more uniform distribution of the doping components within the powder, rather than simply adhering to the surface of a small number of particles through simple mechanical means before molding.

[0057] When the sintering temperature is below 1300℃, the migration of matter between powder particles may be insufficient, leaving many interconnected pores in the green body, making it difficult to form an electrolyte that meets the requirements for airtightness. When the sintering temperature is above 1500℃, excessive grain growth may occur, increasing sintering energy consumption and potentially causing ceramic deformation due to excessive shrinkage. Therefore, controlling the sintering temperature between 1300 and 1500℃ and holding it at that temperature for 2 to 5 hours provides sufficient temperature and time conditions for the densification of the green body.

[0058] The heating and cooling rates for sintering are both 150–250 °C / h, preferably 200 °C / h. During the heating process, different regions of the formed green body should maintain a relatively uniform temperature change to avoid the outer layer shrinking before the interior has fully heated up. During the cooling process after sintering, excessive temperature differences between the surface and interior of the ceramic body should also be avoided. By controlling the heating and cooling rates, the possibility of cracks, warping, or localized peeling caused by thermal stress in the sintered body can be reduced.

[0059] After sintering, a modified 8YSZ electrolyte is obtained. The resulting electrolyte can be an independent electrolyte ceramic sheet or processed into an electrolyte layer of appropriate size according to the subsequent battery structure. It should be noted that the "electrolyte layer" here does not necessarily have to be formed directly on the electrode surface by coating. The independent ceramic sheet prepared by the method of this invention, after being assembled into a solid oxide fuel cell, also constitutes the electrolyte layer between the anode and cathode.

[0060] The YSZ electrolyte prepared by the above method comprises an 8YSZ matrix formed from ZrO2 and Y2O3, and introduced potassium, rubidium, lithium, or sodium elements. The 8YSZ matrix provides the electrolyte with the basic oxygen ion conduction structure, chemical stability, and mechanical support, while potassium, rubidium, lithium, or sodium elements are used to modify the 8YSZ system. The introduction of appropriate amounts of metal elements can alter the local lattice environment and oxygen vacancy distribution of YSZ, thereby reducing the resistance to oxygen ion migration; simultaneously, their role in the sintering process is beneficial to improving the density of the ceramic body. Furthermore, these two aspects correspond to the electrolyte's ion conduction performance and gas-tight structure, respectively, and therefore should not be confused as the same process.

[0061] The obtained YSZ electrolyte can be applied to solid oxide fuel cells (SOFCs). A solid oxide fuel cell includes an anode, a cathode, and an electrolyte layer disposed between the anode and cathode, the electrolyte layer being formed from the aforementioned YSZ electrolyte. It should be noted that "disposed between the anode and cathode" means that the electrolyte layer separates the anode and cathode in the thickness direction or ion transport direction of the cell, preventing direct contact between them. One side of the electrolyte layer is in direct contact with the anode or connected through a functional transition layer, while the other side is in direct contact with the cathode or connected through a barrier layer.

[0062] During battery operation, oxygen on the cathode side gains electrons in the cathode reaction region and forms oxygen ions. These oxygen ions migrate through the YSZ electrolyte layer to the anode side, where they react with the fuel. Due to the electrolyte layer's electronic insulation and oxygen ion conductivity, electrons cannot directly return to the anode through the electrolyte layer; instead, they need to be transported through an external circuit to form a usable current. Therefore, the density of the YSZ electrolyte layer prevents direct mixing of the anode fuel gas and the cathode oxidizing gas, while its oxygen ion conductivity determines the resistance to oxygen ion migration through the electrolyte layer.

[0063] In one alternative structure, a GDC barrier layer can be disposed between the YSZ electrolyte layer and the cathode. GDC is gadolinium oxide-doped cerium oxide, and this barrier layer is used to reduce interfacial reactions and elemental cross-diffusion between the YSZ electrolyte and the cathode material during high-temperature preparation or operation. The anode can be disposed on the side of the YSZ electrolyte layer away from the GDC barrier layer, and the cathode can be disposed on the side of the GDC barrier layer away from the YSZ electrolyte layer. In this structure, the GDC barrier layer is a functional layer between the electrolyte layer and the cathode, and does not change the overall positional relationship of the YSZ electrolyte layer between the anode and cathode.

[0064] The anode can be a composite anode catalyst layer formed of NiO and GDC, and the cathode can be a cathode catalyst layer formed of lanthanum, strontium, and cobalt oxides. The specific materials, thicknesses, and formation methods of the anode and cathode can be adjusted according to the design requirements of the solid oxide fuel cell, as long as the potassium and / or rubidium modified 8YSZ obtained by the method of this invention is used as the electrolyte layer between the anode and cathode.

[0065] It should be noted that the aforementioned description of the final electrolyte as "potassium, rubidium, lithium, or sodium-modified 8YSZ" is intended to indicate the source of the modifying elements and the main composition of 8YSZ. It does not imply that the sintered electrolyte still exists in the form of intact potassium nitrate or rubidium nitrate molecules. Potassium nitrate and rubidium nitrate are precursor salts used in the preparation process. During crystallization, the first heat treatment, the second heat treatment, and sintering, nitrate-related components decompose or are removed, while potassium and / or rubidium are retained and distributed within the YSZ system. Therefore, the amount of doped salt added is expressed as the molar amount of potassium nitrate and / or rubidium nitrate, while the final product is expressed as a potassium, rubidium, lithium, or sodium-modified YSZ electrolyte. These two expressions correspond to the raw material stage and the product stage, respectively, and there is no contradiction.

[0066] It should also be noted that the aforementioned process of first obtaining "YSZ electrolyte powder modified with potassium, rubidium, lithium, or sodium elements," followed by molding and sintering to obtain "YSZ electrolyte," involves two steps. The former is an intermediate powder product capable of being pressed and molded, while the latter is a ceramic electrolyte product that has undergone high-temperature densification. Although the electrolyte powder already contains YSZ-related phases and modifying elements, its particles are still in a loosely packed state and cannot be directly used as a dense electrolyte layer to isolate the anode and cathode gases. Only after dry pressing and high-temperature sintering do the interparticle porosities decrease and a continuous ceramic structure is formed, resulting in a YSZ electrolyte suitable for use in solid oxide fuel cells.

[0067] The first heat treatment, second heat treatment, and final sintering each have different technical functions. The first heat treatment is mainly used to remove organic matter and pulverize the solid precursor; the second heat treatment is mainly used to further transform the pulverized precursor into modified YSZ electrolyte powder in an air atmosphere; and the final sintering is used to densify the formed green body. The objects being treated, the temperature range, and the direct effects of the three processes are all different. Even if the same heating equipment is used in actual production to complete two of the processes sequentially, they should be regarded as different treatment steps according to the corresponding temperature and process stage, and the function of any one of the treatment stages cannot be omitted.

[0068] In summary, through the aforementioned continuous process, zirconium salt, yttrium salt, and doped salt first form a homogeneous precursor solution in a mixed solvent, which then co-crystallizes to form a solid precursor. A first heat treatment removes organic matter and pulverizes the precursor. A second heat treatment further transforms the inorganic components, forming modified YSZ electrolyte powder. Grinding improves the uniformity of the powder's formation. Dry pressing imparts a predetermined shape and initial strength to the powder. Finally, sintering densifies the green body and forms a ceramic electrolyte layer capable of isolating fuel gases and oxidizing gases. These steps are functionally interconnected, collectively achieving the uniform introduction of potassium and / or rubidium elements into 8YSZ and the formation of the electrolyte ceramic body.

[0069] The technical solution of the present invention will be further described below with reference to the embodiments. In the following embodiments, 8YSZ refers to yttrium-stabilized zirconium oxide with ZrO2 and Y2O3 as the main oxides, wherein the molar percentage of ZrO2 is 92% and the molar percentage of Y2O3 is 8%. Unless otherwise specified, the raw materials and equipment used can be obtained through conventional commercial means. The specific parameters below are used to illustrate the present invention, but should not be construed as limiting the scope of protection of the present invention.

[0070] Example 1: This embodiment provides a method for preparing a lithium-modified YSZ electrolyte (Li-YSZ electrolyte). Zirconium acetate (Zr(CH3COO)4) and yttrium nitrate hexahydrate (Y(NO3)3·6H2O) are weighed according to a stoichiometric ratio of ZrO2 to Y2O3 of 92:8. Lithium nitrate is used as the dopant salt, and its amount is 5.3% of the total amount of ZrO2 and Y2O3 constituting YSZ.

[0071] A mixed solvent was prepared according to the molar ratio of N,N-dimethylformamide, ethanol, and deionized water of 1.4:0.62:0.5. Zirconium acetate, yttrium nitrate hexahydrate, and lithium nitrate were weighed and added to the mixed solvent. The mixture was magnetically stirred at 200 rpm for 10 hours at 50°C to ensure that the zirconium acetate, yttrium nitrate hexahydrate, and lithium nitrate were dissolved and uniformly mixed, yielding a precursor solution with a total metal ion concentration of 0.1 mol / L.

[0072] The obtained precursor solution was heated to 100°C and continuously magnetically stirred at 200 rpm at this temperature. As the mixed solvent and water were gradually removed, the concentration of the precursor solution gradually increased and crystallization occurred until the precursor solution transformed into a solid crystal, yielding a solid precursor containing zirconium, yttrium, and lithium components.

[0073] The obtained solid precursor was placed on a heating plate at 300°C for a first heat treatment, which gradually removed residual organic matter and transformed the solid precursor into powdered material. The powdered solid precursor after the first heat treatment was collected and placed in an air furnace for a second heat treatment. The second heat treatment temperature was 600°C, the holding time was 3 hours, and the heating and cooling rates were both 200°C / h.

[0074] After the second heat treatment is completed, the material is cooled, the product of the second heat treatment is collected, and it is ground in a mortar for 30 minutes to break up the agglomerates formed during the second heat treatment, thus obtaining Li-YSZ electrolyte powder.

[0075] The obtained Li-YSZ electrolyte powder was loaded into a circular tableting mold and dry-pressed under 20 MPa pressure using a tableting machine to obtain a disc-shaped blank with a diameter of approximately 20 mm and a thickness of approximately 1 mm. The obtained blank was placed in a high-temperature sintering furnace and sintered at 1500℃ for 3 hours. The heating and cooling rates during the sintering process were both 200℃ / h, resulting in lithium-modified YSZ electrolyte ceramic sheets.

[0076] The diameter of the Li-YSZ electrolyte ceramic sheet obtained after sintering is approximately 17 mm, and its radial shrinkage rate is approximately 15% compared to the pre-sintering blank with a diameter of approximately 20 mm. The obtained Li-YSZ electrolyte ceramic sheet has a dense structure and does not experience gas leakage.

[0077] Example 2: This embodiment provides a method for preparing sodium-modified YSZ electrolyte (Na-YSZ electrolyte). The preparation steps and process parameters are basically the same as those in Example 1, except that sodium nitrate is used instead of lithium nitrate in Example 1.

[0078] Specifically, zirconium acetate and yttrium nitrate hexahydrate were weighed according to the stoichiometric ratio of ZrO2 to Y2O3 of 92:8, with sodium nitrate as the dopant salt. The amount of sodium nitrate was 5.3% of the total amount of ZrO2 and Y2O3 constituting YSZ.

[0079] A mixed solvent was prepared according to the molar ratio of N,N-dimethylformamide, ethanol, and deionized water of 1.4:0.62:0.5. Zirconium acetate, yttrium nitrate hexahydrate, and sodium nitrate were added to the mixed solvent, and the mixture was magnetically stirred at 200 rpm for 10 hours at 50°C to obtain a precursor solution with a total metal ion concentration of 0.1 mol / L.

[0080] The obtained precursor solution was continuously magnetically stirred at 200 rpm at 100°C until the precursor solution was completely crystallized to obtain a solid precursor. Subsequently, the obtained solid precursor was placed on a heating plate at 300°C for a first heat treatment to remove organic matter and pulverize the solid precursor.

[0081] The powdered solid precursor after the first heat treatment was placed in an air furnace and subjected to a second heat treatment at 600°C for 3 hours, with both the heating and cooling rates at 200°C / h. After the product of the second heat treatment cooled, it was ground in a mortar for 30 minutes to obtain Na-YSZ electrolyte powder.

[0082] The obtained Na-YSZ electrolyte powder was dry-pressed under a pressure of 20 MPa to obtain a disc-shaped blank with a diameter of approximately 20 mm and a thickness of approximately 1 mm. The obtained blank was sintered at 1500℃ for 3 hours, with a heating rate and a cooling rate of 200℃ / h, to obtain a YSZ electrolyte ceramic sheet modified with sodium.

[0083] The resulting Na-YSZ electrolyte ceramic sheet after sintering had a diameter of approximately 17.5 mm and a radial shrinkage rate of approximately 12.5%. The resulting Na-YSZ electrolyte ceramic sheet still contained internal pores, exhibiting a relatively porous overall structure and exhibiting gas leakage. Although this embodiment employed the same liquid-phase precursor preparation route as Example 1, sodium modification did not achieve sufficient densification of the YSZ electrolyte ceramic sheet under the aforementioned sintering conditions.

[0084] Example 3: This embodiment provides a method for preparing potassium-modified YSZ electrolyte (K-YSZ electrolyte). The preparation steps and process parameters are basically the same as those in Example 1, except that potassium nitrate is used instead of lithium nitrate in Example 1.

[0085] Based on the stoichiometric relationship of ZrO2 to Y2O3 (92:8 molar ratio), zirconium acetate and yttrium nitrate hexahydrate were weighed, with potassium nitrate as the dopant salt. The amount of potassium nitrate was 5.3% of the total amount of ZrO2 and Y2O3 constituting YSZ.

[0086] A mixed solvent was prepared according to the molar ratio of N,N-dimethylformamide, ethanol, and deionized water of 1.4:0.62:0.5. Zirconium acetate, yttrium nitrate hexahydrate, and potassium nitrate were added to the mixed solvent, and the mixture was magnetically stirred at 200 rpm for 10 hours at 50°C to ensure that all solutes were fully dissolved and homogeneously mixed, resulting in a precursor solution with a total metal ion concentration of 0.1 mol / L.

[0087] The obtained precursor solution was continuously magnetically stirred at 200 rpm at 100°C until the precursor solution was completely crystallized to obtain a solid precursor. The obtained solid precursor was placed on a heating plate at 300°C for a first heat treatment to remove organic matter and pulverize the solid precursor.

[0088] The powdered solid precursor was placed in an air furnace and subjected to a second heat treatment at 600°C for 3 hours, with both the heating and cooling rates at 200°C / h. After the product from the second heat treatment cooled, it was ground in a mortar for 30 minutes to obtain K-YSZ electrolyte powder.

[0089] The obtained K-YSZ electrolyte powder was dry-pressed under a pressure of 20 MPa to obtain a disc-shaped blank with a diameter of approximately 20 mm and a thickness of approximately 1 mm. Subsequently, the obtained blank was placed in a high-temperature sintering furnace and sintered at 1500℃ for 3 hours, with a heating rate and a cooling rate of 200℃ / h, to obtain potassium-modified YSZ electrolyte ceramic sheets.

[0090] The diameter of the K-YSZ electrolyte ceramic sheet obtained after sintering is approximately 18 mm, and the radial shrinkage rate is approximately 10%. The obtained K-YSZ electrolyte ceramic sheet has a dense structure and does not leak gas, indicating that under the preparation conditions of this embodiment, the addition of potassium nitrate is beneficial to the formation of an airtight structure of the YSZ electrolyte ceramic sheet.

[0091] Example 4: This embodiment provides a method for preparing a rubidium-modified YSZ electrolyte (Rb-YSZ electrolyte). The preparation steps and process parameters are basically the same as those in Example 1, except that rubidium nitrate is used instead of lithium nitrate in Example 1.

[0092] Based on the stoichiometric relationship of ZrO2 to Y2O3 (92:8 molar ratio), zirconium acetate and yttrium nitrate hexahydrate were weighed, with rubidium nitrate as the dopant salt. The amount of rubidium nitrate was 5.3% of the total amount of ZrO2 and Y2O3 constituting YSZ.

[0093] A mixed solvent was prepared according to the molar ratio of N,N-dimethylformamide, ethanol, and deionized water of 1.4:0.62:0.5. Zirconium acetate, yttrium nitrate hexahydrate, and rubidium nitrate were added to the mixed solvent, and the mixture was magnetically stirred at 200 rpm for 10 hours at 50°C to obtain a precursor solution with a total metal ion concentration of 0.1 mol / L.

[0094] The obtained precursor solution was continuously magnetically stirred at 200 rpm at 100°C until the precursor solution was completely crystallized to obtain a solid precursor. The obtained solid precursor was placed on a heating plate at 300°C for a first heat treatment to remove organic matter and pulverize the solid precursor.

[0095] The powdered solid precursor was placed in an air furnace and subjected to a second heat treatment at 600°C for 3 hours, with both the heating and cooling rates at 200°C / h. After the product from the second heat treatment cooled, it was ground in a mortar for 30 minutes to obtain Rb-YSZ electrolyte powder.

[0096] The obtained Rb-YSZ electrolyte powder was dry-pressed under a pressure of 20 MPa to obtain a disc-shaped blank with a diameter of approximately 20 mm and a thickness of approximately 1 mm. The obtained blank was placed in a high-temperature sintering furnace and sintered at 1500℃ for 3 hours, with a heating rate and a cooling rate of 200℃ / h, to obtain a YSZ electrolyte ceramic sheet modified with rubidium.

[0097] The diameter of the Rb-YSZ electrolyte ceramic sheet obtained after sintering is approximately 17 mm, and the radial shrinkage rate is approximately 15%. The obtained Rb-YSZ electrolyte ceramic sheet has a dense structure and does not experience gas leakage.

[0098] Comparative Example 1: This comparative example provides a method for preparing an unmodified YSZ electrolyte. It uses the same zirconium salt, yttrium salt, mixed solvent, and the same stirring, crystallization, first heat treatment, second heat treatment, grinding, molding, and sintering conditions as Example 1. The difference is that this comparative example does not add lithium nitrate, sodium nitrate, potassium nitrate, rubidium nitrate, or other doped salts.

[0099] Based on the stoichiometric relationship of ZrO2 to Y2O3 (92:8 molar ratio), zirconium acetate and yttrium nitrate hexahydrate were weighed and dissolved together in a mixed solvent composed of N,N-dimethylformamide, ethanol, and deionized water. The molar ratio of N,N-dimethylformamide, ethanol, and deionized water was 1.4:0.62:0.5. The solution was magnetically stirred at 200 rpm for 10 hours at 50°C to obtain the precursor solution.

[0100] The obtained precursor solution was continuously magnetically stirred at 200 rpm at 100°C until complete crystallization to obtain a solid precursor. The obtained solid precursor was placed on a heating plate at 300°C for a first heat treatment to remove organic matter and pulverize the solid precursor. Subsequently, the pulverized solid precursor was placed in an air furnace and subjected to a second heat treatment at 600°C for 3 hours, with both the heating and cooling rates being 200°C / h.

[0101] The second heat-treated product was ground in a mortar for 30 minutes to obtain unmodified YSZ electrolyte powder. The obtained YSZ electrolyte powder was dry-pressed under a pressure of 20 MPa to obtain a disc-shaped green body with a diameter of approximately 20 mm and a thickness of approximately 1 mm. The obtained green body was sintered at 1500℃ for 3 hours, with a heating rate and a cooling rate of 200℃ / h, to obtain unmodified YSZ electrolyte ceramic sheets.

[0102] The diameter of the unmodified YSZ electrolyte ceramic sheet obtained after sintering was approximately 17.5 mm, and the radial shrinkage rate was approximately 12.5%. The obtained electrolyte ceramic sheet had a porous structure and exhibited gas leakage, indicating that the unmodified YSZ electrolyte ceramic sheet did not achieve sufficient densification under the sintering conditions of this comparative example.

[0103] The sintered electrolyte ceramic sheets obtained in Examples 1-4 and Comparative Example 1 are shown below. Figure 1 As shown. By Figure 1 It can be seen that, under the same molding size and sintering conditions, the electrolyte ceramic sheets corresponding to different modified elements all underwent a certain degree of sintering shrinkage. Among them, the Li-YSZ electrolyte ceramic sheet obtained in Example 1, the K-YSZ electrolyte ceramic sheet obtained in Example 3, and the Rb-YSZ electrolyte ceramic sheet obtained in Example 4 were able to form air-leakage ceramic sheets; the Na-YSZ electrolyte ceramic sheet obtained in Example 2 and the unmodified YSZ electrolyte ceramic sheet obtained in Comparative Example 1 still exhibited porous air leakage.

[0104] Application example: Solid oxide fuel cell (SOFC) single cells were assembled using the electrolyte ceramic sheets obtained in the above embodiments as electrolyte layers.

[0105] First, a GDC barrier layer slurry was prepared. Gadolinium oxide-doped cerium oxide powder, polyvinyl butyral, and N-methylpyrrolidone were mixed at a mass ratio of 0.95:0.05:1 and centrifuged at 2000 rpm for 10 minutes to obtain a homogeneous GDC slurry. The obtained GDC slurry was spin-coated onto one side of an electrolyte ceramic sheet at 5000 rpm for 10 seconds. Subsequently, the electrolyte ceramic sheet coated with the GDC slurry was dried on a heater at 200°C and then calcined in air at 1300°C for 2 hours to form a dense GDC barrier layer. The GDC barrier layer is located between the electrolyte layer and the cathode catalyst layer to suppress elemental cross-diffusion between the two.

[0106] NiO, GDC, polyvinyl butyral, and N-methylpyrrolidone were mixed in a mass ratio of 1.57:1:0.29:0.63 and centrifuged at 2000 rpm to obtain a homogeneous anode slurry. The resulting anode slurry was spin-coated onto the side of the electrolyte ceramic sheet without the GDC barrier layer and calcined in air at 1200°C for 3 hours to form a NiO / GDC anode catalyst layer.

[0107] Lanthanum strontium cobalt oxide powder, polyvinyl butyral, and N-methylpyrrolidone were mixed at a mass ratio of 0.9:0.1:0.8 and centrifuged at 2000 rpm to obtain a homogeneous cathode slurry. The obtained cathode slurry was coated onto a GDC barrier layer, dried in a heater at 160°C for 30 minutes, and then calcined in air at 900°C for 2 hours to form an LSC cathode catalyst layer, thereby obtaining a solid oxide fuel cell single cell comprising an anode catalyst layer, an electrolyte layer, a GDC barrier layer, and a cathode catalyst layer.

[0108] Test Example 1: Phase analysis was performed on the electrolyte ceramic sheets obtained in Examples 1-4 and Comparative Example 1 using an X-ray diffractometer equipped with a Cu Kα radiation source. The scanning range of the diffraction angle 2θ was 10°–80°, the scanning step size was 0.02°, and the scanning rate was 20° / min. The obtained XRD patterns are shown below. Figure 2 As shown.

[0109] Depend on Figure 2 It can be seen that the main diffraction peaks of Li-YSZ obtained in Example 1, Na-YSZ obtained in Example 2, K-YSZ obtained in Example 3, Rb-YSZ obtained in Example 4, and the unmodified YSZ obtained in Comparative Example 1 all correspond to the cubic fluorite structure of 8YSZ, and no obvious monoclinic phase diffraction peaks or other impurity phase diffraction peaks were observed. The above results indicate that under the modification ratio and preparation conditions of this example, the introduction of lithium, sodium, potassium, and rubidium elements did not significantly change the main crystal phase structure of YSZ, nor did it form a second phase that could be clearly identified by the XRD test.

[0110] Further elemental and chemical state analysis of the electrolyte ceramic sheets obtained in Examples 1-4 and Comparative Example 1 was performed using X-ray photoelectron spectroscopy. The test results are as follows: Figure 3 As shown. Among them, Figure 3 In the figure, 'a' shows the Y 3d5 / 2 energy spectrum of each sample. Figure 3 b in the figure shows the Zr 3d5 / 2 energy spectrum of each sample. Figure 3 c in the figure shows the O 1s energy spectrum of each sample. Figure 3 The d values ​​in the figure represent the Li 1s energy spectrum in Example 1, the Na 1s energy spectrum in Example 2, the K 2p3 / 2 energy spectrum in Example 3, and the Rb 3d5 / 2 energy spectrum in Example 4, respectively.

[0111] Depend on Figure 3 As can be seen from 'd', characteristic signals of lithium, sodium, potassium, and rubidium were detected in the electrolyte ceramic sheets obtained in Examples 1-4, indicating that the corresponding modifying elements have been introduced into the YSZ electrolyte system. Figure 3 As shown in a to c, compared with unmodified YSZ, the binding energy peaks corresponding to Y, Zr and O in modified YSZ are shifted to a certain extent, indicating that the introduction of the modifying elements has affected the local oxidation state of yttrium, zirconium and oxygen in YSZ.

[0112] Test Example 2: The microstructure of the electrolyte ceramic sheets obtained in Examples 1-4 and Comparative Example 1 was observed using focused ion beam scanning electron microscopy. The cross-sectional morphology of the unmodified YSZ electrolyte ceramic sheet obtained in Comparative Example 1 is shown below. Figure 4 As shown, the cross-sectional morphology of the Na-YSZ electrolyte ceramic sheet obtained in Example 2 is as follows. Figure 6 As shown.

[0113] Depend on Figure 4 and Figure 6 It can be seen that both the unmodified YSZ electrolyte ceramic sheet and the Na-YSZ electrolyte ceramic sheet contain numerous fine and interconnected pores, indicating that the two types of ceramic sheets were not fully densified after sintering at 1500℃. These interconnected pores can form gas channels penetrating the electrolyte layer, leading to gas leakage from the ceramic sheet.

[0114] The cross-sectional morphology and surface morphology of the Li-YSZ electrolyte ceramic sheet obtained in Example 1 are as follows: Figure 5 and Figure 9 As shown. By Figure 5 It can be seen that the Li-YSZ electrolyte ceramic sheet still contains some relatively large isolated pores, but no large-scale interconnected pores have been formed. Figure 9It can be seen that the surface of the Li-YSZ electrolyte ceramic sheet is generally continuous, and no obvious through cracks were observed. Therefore, the Li-YSZ electrolyte ceramic sheet obtained in Example 1 can maintain its airtightness.

[0115] The cross-sectional morphologies of the K-YSZ electrolyte ceramic sheet obtained in Example 3 and the Rb-YSZ electrolyte ceramic sheet obtained in Example 4 are as follows: Figure 7 and Figure 8 As shown. By Figure 7 and Figure 8 It can be seen that both K-YSZ and Rb-YSZ electrolyte ceramic sheets have relatively dense cross-sectional structures and uniform grain distribution, with no large-scale through-pores observed. These results indicate that, under the same forming and sintering conditions, potassium and rubidium modification is beneficial for promoting the densification of 8YSZ electrolyte ceramic sheets during sintering.

[0116] The results showed that the K-YSZ electrolyte ceramic sheet obtained in Example 3 and the Rb-YSZ electrolyte ceramic sheet obtained in Example 4 both had good compactness and relatively uniform grain size, and no large-scale interconnected pores leading to gas penetration were observed. The Li-YSZ electrolyte ceramic sheet obtained in Example 1 contained some isolated pores, but no large-scale interconnected pores were formed, therefore no gas leakage occurred.

[0117] Both the Na-YSZ electrolyte ceramic sheet obtained in Example 2 and the unmodified YSZ electrolyte ceramic sheet obtained in Comparative Example 1 contained numerous fine through-pores, and even after sintering at 1500℃, sufficient densification was not achieved, resulting in gas leakage. These results indicate that, under the same precursor preparation, heat treatment, forming, and sintering conditions, different monovalent metal elements have varying effects on the densification of YSZ electrolytes during sintering. Potassium and rubidium modification, in particular, enabled the resulting electrolyte ceramic sheets to form a relatively dense, gas-tight structure.

[0118] Test Example 3: The electrochemical performance of the electrolyte ceramic sheets obtained in Examples 1-4 and Comparative Example 1, as well as the solid oxide fuel cell single cells assembled from the corresponding electrolyte ceramic sheets, was tested using a solid oxide fuel cell testing system.

[0119] During the test, hydrogen gas with a humidity of 3 vol.% was introduced into the anode side of the single cell at a flow rate of 85 sccm; air was introduced into the cathode side at a flow rate of 85 sccm. Electrochemical impedance spectroscopy was used to test the impedance performance of the electrolyte layer and the single cell. The test frequency range was 0.1 Hz to 100 kHz, the AC perturbation amplitude was 10 mV, and the test temperatures were 800℃, 700℃, 600℃, 500℃, and 400℃, respectively.

[0120] 1. Ohmic resistance and activation energy analysis The ohmic resistance data obtained at different temperatures were analyzed. The test results of ohmic resistance and oxygen ion migration activation energy of different YSZ electrolyte ceramic sheets obtained in Examples 1-4 and Comparative Example 1 are as follows: Figure 10 As shown. Figure 10 The horizontal axis represents the reciprocal of absolute temperature, 1000 / T, where T is the test temperature in Kelvin (K). A larger horizontal axis value indicates a lower test temperature. The vertical axis represents the common logarithm of the electrolyte's ohmic surface resistance after temperature correction, i.e., lg(R0 / T). ohm / T), where R ohm Ohmic surface resistance, unit is Ω·cm 2 By performing linear fitting on test points at different temperatures, the activation energy Ea for oxygen ion migration can be calculated based on the slope of the fitted line. A smaller slope generally indicates a lower activation energy and easier oxygen ion migration.

[0121] Depend on Figure 10 It is evident that different monovalent metal elements have different effects on the migration performance of oxygen ions in YSZ electrolytes. The activation energies for oxygen ion migration of the Li-YSZ electrolyte obtained in Example 1 and the Rb-YSZ electrolyte obtained in Example 4 are both lower than those of the unmodified YSZ electrolyte obtained in Comparative Example 1, indicating that the introduction of lithium and rubidium can reduce the energy barrier that needs to be overcome for oxygen ion migration to a certain extent.

[0122] At a lower test temperature, the ohmic resistance of the Rb-YSZ electrolyte obtained in Example 4 was lower than that of the unmodified YSZ electrolyte obtained in Comparative Example 1, indicating that rubidium modification is beneficial to reducing the oxygen ion migration resistance under low temperature conditions.

[0123] It should be noted that, Figure 10 This is used to reflect the influence trend of different modification elements on the ohmic resistance and activation energy of YSZ electrolyte; subsequent single-cell electrochemical impedance spectroscopy and voltammetric performance testing also require that the electrolyte ceramic sheet has sufficient density and airtightness.

[0124] 2. Electrochemical impedance spectroscopy analysis The Na-YSZ electrolyte ceramic sheet obtained in Example 2 and the unmodified YSZ electrolyte ceramic sheet obtained in Comparative Example 1 did not achieve sufficient densification after sintering at 1500℃. There were through pores inside the ceramic sheet and gas leakage occurred. Therefore, it was impossible to assemble a single cell that could be tested normally using the above two electrolyte ceramic sheets, and it was also impossible to obtain an effective single cell electrochemical impedance spectrum.

[0125] Therefore, solid oxide fuel cell single cells were assembled using the Li-YSZ electrolyte ceramic sheet obtained in Example 1, the K-YSZ electrolyte ceramic sheet obtained in Example 3, and the Rb-YSZ electrolyte ceramic sheet obtained in Example 4, respectively, and electrochemical impedance spectroscopy (EIS) was performed at 800°C. The resulting Nyquist spectra are shown below. Figure 11 As shown in the figure. The horizontal axis Z′ represents the real part of the impedance, which mainly reflects the actual resistance caused by the electrolyte, electrodes and connection points; the vertical axis is usually written as -Z″, which represents the negative value of the imaginary part of the impedance, mainly reflecting the phase response generated by electrode reaction, interface capacitance and mass transfer process. Figure 11 Each data point in the graph corresponds to an AC test frequency, and the curve typically extends from the high-frequency region on the left to the low-frequency region on the right. The intersection of the high-frequency end of the curve with the horizontal axis represents the ohmic resistance of the single cell, mainly including the electrolyte bulk resistance and contact resistance. When the curve intersects the horizontal axis again at the low-frequency end, the difference in the horizontal axis between the low-frequency intersection and the high-frequency intersection can be used to characterize the polarization resistance of the single cell, mainly reflecting the resistance generated by electrode reactions and interfacial mass transfer processes.

[0126] Depend on Figure 11 It can be seen that single cells assembled using Li-YSZ electrolyte, K-YSZ electrolyte, and Rb-YSZ electrolyte can all obtain effective electrochemical impedance spectroscopy. The ohmic resistances corresponding to Li-YSZ electrolyte, K-YSZ electrolyte, and Rb-YSZ electrolyte are 4.55 Ω·cm. 2 3.63 Ω·cm 2 and 3.80 Ω·cm 2 .

[0127] Among the three electrolytes mentioned above, K-YSZ electrolyte exhibits the lowest ohmic resistance, followed by Rb-YSZ electrolyte, while Li-YSZ electrolyte shows a relatively high ohmic resistance. These results indicate that, under the same single-cell structure and testing conditions, potassium and rubidium modification can maintain a low ohmic resistance in the 8YSZ electrolyte. Specifically, the potassium-modified electrolyte exhibits lower oxygen ion migration resistance at 800℃.

[0128] 3. Volt-ampere performance analysis The volt-ampere performance of solid oxide fuel cell single cells assembled using the Li-YSZ electrolyte ceramic sheet obtained in Example 1, the K-YSZ electrolyte ceramic sheet obtained in Example 3, and the Rb-YSZ electrolyte ceramic sheet obtained in Example 4 were tested at 800℃. The obtained volt-ampere characteristic curves are shown below. Figure 12 As shown.

[0129] Depend on Figure 12 It can be seen that as the current density gradually increases, the output voltage of the single cell using Li-YSZ, K-YSZ and Rb-YSZ electrolytes gradually decreases, indicating that all three types of single cells can output electrical energy under external load conditions.

[0130] At the same or similar current density, single cells assembled with Rb-YSZ electrolyte exhibit a higher overall output voltage, followed by those assembled with K-YSZ electrolyte, while those assembled with Li-YSZ electrolyte have a relatively lower output voltage. Furthermore, single cells assembled with Rb-YSZ electrolyte also demonstrate a higher open-circuit voltage.

[0131] The above results demonstrate that the electrolyte ceramic sheets obtained in Examples 1, 3, and 4 can all form an airtight electrolyte layer and can be used to assemble solid oxide fuel cells capable of generating electricity normally. Specifically, the rubidium-modified 8YSZ electrolyte is beneficial for improving the open-circuit voltage and output voltage of a single cell, while the potassium-modified 8YSZ electrolyte exhibits lower ohmic resistance.

[0132] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that the present invention includes, but is not limited to, the contents described in the accompanying drawings and the specific embodiments above. Any modifications that do not depart from the functional and structural principles of the present invention will be included within the scope of the claims.

Claims

1. A method for preparing a YSZ electrolyte, characterized in that, include: Zirconium salt, yttrium salt, and dopant salt are dissolved together in a mixed solvent to obtain a precursor solution. The zirconium salt and yttrium salt are mixed according to the stoichiometric ratio of 8YSZ, where the molar ratio of ZrO2 to Y2O3 in 8YSZ is 92:

8. The molar amount of the dopant salt to the total molar amount of Y2O3 and ZrO2 in 8YSZ is (3-8):

100. The dopant salt is selected from lithium nitrate, sodium nitrate, potassium nitrate, or rubidium nitrate. The mixed solvent includes N,N-dimethylformamide, ethanol, and deionized water, and the molar ratio of N,N-dimethylformamide, ethanol, and deionized water in the mixed solvent is (1.0-2.0):(0.4-0.8):(0.3-0.7). The precursor solution is heated under stirring conditions to crystallize the precursor solution and obtain a solid precursor. The solid precursor is subjected to a first heat treatment to remove organic matter from the solid precursor and to pulverize the solid precursor; The powdered solid precursor is subjected to a second heat treatment in an air atmosphere, and the product of the second heat treatment is ground to obtain YSZ electrolyte powder. The temperature of the first heat treatment is 250-350°C; the temperature of the second heat treatment is 550-650°C, and the treatment time is 2-5 hours. The YSZ electrolyte powder is sequentially shaped and sintered to obtain the YSZ electrolyte, wherein the YSZ electrolyte is an 8YSZ electrolyte modified by the metal elements contained in the doped salt.

2. The method for preparing YSZ electrolyte according to claim 1, characterized in that, The zirconium salt is zirconium acetate, and the yttrium salt is yttrium nitrate hexahydrate.

3. The method for preparing YSZ electrolyte according to claim 1, characterized in that, The total concentration of metal ions in the precursor solution is 0.05–0.2 mol / L.

4. The method for preparing YSZ electrolyte according to claim 1, characterized in that, The mixture of the zirconium salt, the yttrium salt, the doped salt, and the mixed solvent is stirred at 40–70°C for 6–15 hours to obtain the precursor solution.

5. The method for preparing YSZ electrolyte according to claim 4, characterized in that, The step of heating the precursor solution under stirring conditions includes: continuously stirring the precursor solution at 80-120°C until crystallization occurs, thereby obtaining the solid precursor.

6. The method for preparing YSZ electrolyte according to claim 1, characterized in that, The grinding time for the product of the second heat treatment is 20 to 60 minutes.

7. The method for preparing YSZ electrolyte according to claim 6, characterized in that, The forming process is dry pressing, with a pressure of 15–30 MPa; the sintering temperature is 1300–1500°C, and the sintering time is 2–5 hours; the heating and cooling rates of the second heat treatment and the sintering are both 150–250°C / h.

8. A YSZ electrolyte, characterized in that, The YSZ electrolyte is prepared by the preparation method according to any one of claims 1 to 7.

9. An SOFC battery, characterized in that, It includes an anode, a cathode, and an electrolyte layer disposed between the anode and the cathode, the electrolyte layer being formed of the YSZ electrolyte of claim 8.

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