High-temperature high-stability double-doped composite electrolyte and preparation method thereof

Abstract

The invention discloses a high-temperature high-stability double-doped composite electrolyte and a preparation method thereof, and belongs to the technical field of solid oxide fuel cells. The high-temperature high-stability double-doped composite electrolyte is prepared by performing double doping on zirconium oxide by yttrium oxide and scandium oxide and compounding aluminum oxide, and is prepared by the following steps: preparing precursor gel from nitrate of zirconium oxide, yttrium oxide and scandium oxide as raw materials by adopting a sol-gel method; adding aluminum oxide nano-powder and then carrying out ball milling to obtain slurry; and sequentially carrying out pre-sintering and high-temperature sintering on the slurry to obtain the composite material. The ionic conductivity of the material at 800 DEG C reaches 0.10 S / cm to 0.12 S / cm, and the breaking strength is gt; the conductivity is attenuated at the temperature of 1000 DEG C for 1000 hours under the pressure of 200 MPa; the thermal expansion coefficient is (9.8 * 10 <-6 >) K <-1 >-(10.2 * 10 <-6 >) K <-1 >.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of solid oxide fuel cells, and particularly relates to a high-temperature and high-stability double-doped composite electrolyte and a preparation method thereof. BACKGROUND

[0002] A solid oxide fuel cell (SOFC) is a high-temperature electrochemical device that realizes fuel oxidation and electrical energy output through oxygen ion conduction, and has the advantages of high energy conversion efficiency (>60%) and fuel diversity (hydrogen, hydrocarbons, etc.). The main components of a solid oxide fuel cell single unit mainly include an electrolyte, an anode or fuel electrode, a cathode or air electrode, and a connecting body or bipolar plate. The electrolyte, as the core component of the SOFC, is required to have high oxygen ion conductivity (>0.1 S / cm), excellent chemical stability, and sufficient mechanical strength (>200 MPa) at 800-1000℃.

[0003] At present, 8mol% yttria-stabilized zirconia (hereinafter referred to as 8YSZ) is the most widely used electrolyte material, and its ion conductivity at 800℃ is about 0.02-0.03 S / cm, and can reach 0.1 S / cm at 1000℃. However, in long-term high-temperature operation, 8YSZ has problems such as grain growth, conductivity decay (10-20% decay in 1000 hours at 1000℃), and mechanical strength reduction (from 250 MPa to below 150 MPa). SUMMARY

[0004] The purpose of the present application is to provide a high-temperature and high-stability double-doped composite electrolyte and a preparation method thereof, which can solve the problems of low conductive ion rate and poor stability of the 8YSZ electrolyte material in the prior art at high temperature.

[0005] To achieve the above purpose, the present application provides a high-temperature and high-stability double-doped composite electrolyte, which comprises zirconia doped with 6-10mol% yttria, zirconia doped with 1-3mol% scandia, and 5-20wt% alumina composite phase.

[0006] Further, it comprises zirconia doped with 8mol% yttria, zirconia doped with 2mol% scandia, and 10wt% alumina composite phase.

[0007] The present application provides a preparation method of a high-temperature and high-stability double-doped composite electrolyte, comprising the following steps: Yttria, zirconia, scandia, and alumina are configured in proportion, nitrate is used as raw material, and a precursor gel is prepared by a sol-gel method; Alumina is added to the precursor gel, and after adding water, composite slurry is prepared by ultrasonic dispersion and ball milling. After the dried composite slurry is sequentially pre-sintered and sintered, a high-temperature and high-stability double-doped composite electrolyte is prepared.

[0008] Further, the sol-gel method comprises the following steps: The nitrate of yttrium oxide, the nitrate of zirconium oxide and the nitrate of scandium oxide are dissolved in water, a cross-linking agent and a solvent are added, and a sol is formed by constant temperature stirring; the sol is dried in vacuum to prepare a precursor gel.

[0009] Further, the molar ratio of the nitrate of zirconium oxide (calculated based on the number of moles of zirconium oxide), the cross-linking agent and the solvent is (0.5-1.5):1:(1-3).

[0010] Further, the molar ratio of the nitrate of zirconium oxide (calculated based on the number of moles of zirconium oxide), the cross-linking agent and the solvent is 0.9:1:1.

[0011] Further, the temperature of constant temperature stirring is 75-90℃, and the time of constant temperature stirring is 4-6h; the temperature of vacuum drying is 120-150℃, and the time of vacuum drying is 15-20h.

[0012] Further, the temperature of constant temperature stirring is 80℃, and the stirring time is 5h to form a gel. Then, the precursor (gel) is prepared by vacuum drying at 130℃ for 18h.

[0013] Further, the particle size of the aluminum oxide is 20-100nm, and the ultrasonic dispersion parameters include: power 100-300W, frequency 20-50kHz, and time 25-40min.

[0014] Further, the dried composite slurry is prepared by vacuum drying at 100-120℃ for 15-24h.

[0015] Further, the temperature of pre-sintering is 600-800℃, the time of pre-sintering is 2.5-4h, and the heating rate is 3-8℃ / min.

[0016] Further, the sintering comprises: adding a binder, dry pressing the material after pre-sintering to shape, and then sintering at 1400-1600℃ for 4.5-6h; wherein the heating rate is 3-8℃ / min; The binder is a polyvinyl alcohol aqueous solution with a content of 4-6wt%, and the dry pressing pressure is 10-20MPa.

[0017] In summary, the present application has the following advantages: The yttrium oxide and scandium oxide are used to double-dope the zirconium oxide base material, and the aluminum oxide is used as a composite phase for compounding, so that the high-temperature conductivity of the double-doped composite electrolyte is successfully increased from 0.02 S / cm-0.03 S / cm of 8YSZ to 0.10 S / cm-0.12 S / cm, which is increased by nearly 3.5-4.8 times, is more close to ScSZ (0.2 S / cm) doped only with scandium (Sc2O3), but greatly reduces the cost. At the same time, the high-temperature high-stability double-doped composite electrolyte prepared in the application has high high-temperature stability, and the decay rate is directly reduced to less than 5% compared with 10%-20% of 8YSZ. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 A flowchart for preparing the high-temperature high-stability double-doped composite electrolyte in the embodiments of the application is shown in the figure. Figure 2 A comparison curve of the ionic conductivities of the composite electrolytes prepared in the embodiments and the comparative examples of the application is shown in the figure. Figure 3 A comparison curve of the thermal expansion coefficients of the composite electrolytes prepared in the embodiments and the comparative examples of the application is shown in the figure. Figure 4 A microstructure diagram of the high-temperature high-stability double-doped composite electrolyte prepared in the embodiments of the application is shown in the figure. Figure 5 A curve of the ionic conductivities of the composite electrolytes of the embodiments and the comparative examples of the application changing with time is shown in the figure. Figure 6 A curve of the mechanical strength of the composite electrolytes of the embodiments and the comparative examples of the application changing with temperature is shown in the figure. DETAILED DESCRIPTION

[0019] The principles and characteristics of the application are described below in combination with embodiments, and the examples are only used to explain the application and not to limit the scope of the application. If the specific conditions are not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturer are used. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased on the market.

[0020] In a first aspect, the application provides a high-temperature high-stability double-doped composite electrolyte, which comprises zirconium oxide with a yttrium oxide doping amount of 6mol%-10mol%, zirconium oxide with a scandium oxide doping amount of 1mol%-3mol%, and 5wt%-20wt% of an aluminum oxide composite phase.

[0021] The high-temperature high-stability double-doped composite electrolyte in the application is double-doped with scandium oxide (Sc2O3) and yttrium oxide (Y2O3) on zirconium oxide (ZrO2), and then compounded with aluminum oxide (Al2O3), which has the following advantages: (1) Synergistic effect of double doping: Compared with single yttria doping (low conductivity, 0.06 S / cm) or single scandia doping (high decay, 10.2%), the double doping method combines the phase stability of Y and the high conductivity of Sc, and the conductivity of the composite electrolyte reaches 0.12 S / cm, and the decay is reduced to 3.8%, realizing performance optimization.

[0022] (2) High temperature stability: The pinning effect of Al2O3 controls the grain size to be 0.5 μm-2 μm, which is better than single doping material.

[0023] (3) High conductivity: Compared with 8YSZ, the conductivity is increased by 3.5-4.8 times (0.10 S / cm-0.12 S / cm at 800°C vs. 0.02 S / cm-0.03 S / cm).

[0024] (4) Excellent stability: The pinning effect of the composite electrolyte added with alumina composite phase is also better than that of the single double-doped electrolyte (without adding alumina composite phase), and the pinning effect of Al2O3 controls the grain size to be 0.5 μm-2 μm, and the decay rate is only 1 / 3 of that of 8YSZ.

[0025] (5) Thermal expansion matching: TEC (9.8×10 -6 ) K -1 ~ (10.2×10 -6 ) K -1 Matches well with electrode material (10×10 -6 ) K -1 ~12×10 -6 ) K -1 , and the TEC of the present application can be adjusted in the range, while the TEC of the electrolyte using single YSZ and alumina composite is uncontrollable.

[0026] In summary, the high-temperature and high-stability double-doped composite electrolyte prepared by the present application can be used as SOFC electrolyte, which improves the battery efficiency and service life, and its high conductivity and stability meet the commercial needs of SOFC. The TEC matching reduces the thermal stress, thereby prolonging the service life of the assembly, and is suitable for high-efficiency and long-life energy conversion devices.

[0027] In a preferred embodiment of the present application, the zirconia is doped with 8 mol% yttria, the zirconia is doped with 2 mol% scandium oxide, and 10 wt% alumina is added as a composite phase. The high-temperature and high-stability double-doped composite electrolyte prepared at this ratio has the following advantages: (1) The highest conductivity (0.12 S / cm), which is nearly 5 times higher than that of traditional 8YSZ (0.025 S / cm), significantly reduces the ohmic loss of the electrolyte, and is suitable for high-power density solid oxide fuel cells. (2) The double-doping (Y+Sc) method optimizes the lattice distortion of zirconia. The introduction of Sc 3+ may reduce the oxygen vacancy migration activation energy, thereby improving the oxygen ion migration rate. (3) Balance of strength and toughness, with a bending strength of 220 MPa, which can combine the dispersion strengthening effect of Al2O3 (10 wt%), so that the fracture toughness of the composite electrolyte is about 50% higher than that of traditional YSZ, meeting the high-temperature mechanical stability requirements. (4) Excellent thermal matching, TEC = 10.0 x 10 -6 K -1 , which is best matched with typical electrode materials (such as Ni-YSZ anode TEC ≈ 10.5 x 10 -6 K -1 ), so as to reduce the risk of interface delamination during thermal cycling. (5) Low attenuation rate (3.8%), long-term stability is significantly better than that of traditional materials (12.5%), which may be due to the fact that double-doping inhibits high-temperature grain boundary segregation, and Al2O3 nanoparticles (10 wt%) pin the grain boundary to delay grain coarsening.

[0028] Although the above-mentioned composition with the above-mentioned ratio is used, the following problems may still exist: For example, studies have shown that ScSZ electrolyte doped with scandium (Sc2O3) can increase the conductivity to 0.2 S / cm (800°C), but the high-temperature phase transition and cost problems limit the application of scandium-doped electrolyte. In addition, the introduction of Al2O3 as a second phase can enhance the stability, but the traditional mechanical mixing method will cause uneven distribution of phases, and the high sintering temperature (>1650°C) will also increase the energy consumption. Based on this, the following solutions are also proposed.

[0029] In a second aspect, based on the general technical concept of the present application, a preparation method of a high-temperature and high-stability double-doped composite electrolyte is also provided, as shown in Figure 1 , comprising the following steps: S1, configuring yttria, zirconia, scandium oxide, and alumina according to the ratio, using nitrate as the raw material, and preparing a precursor gel by a sol-gel method; S2, adding alumina to the precursor gel, then adding water, and preparing a composite slurry after ultrasonic dispersion and ball milling; S3, after drying the composite slurry, pre-sintering and sintering, high-temperature and high-stability double-doped composite electrolyte is prepared.

[0030] The preparation method of the present application has the following advantages: (1) Y 3+ and Sc 3+ Double-doped synergistic effect improves high-temperature stability: in step S1, the introduction of Y(NO3)3·6H2O and Sc(NO3)3 dopes the ZrO2 matrix with double rare earth ions, forming a (Y, Sc) co-stable cubic phase structure (for example, the combination of 8YSZ and ScSZ is optimized), which can significantly improve the following performance: 1) Inhibit phase transition, double-doped is more effective than single Y or Sc doped in stabilizing high-temperature cubic phase (avoiding monoclinic or tetragonal phase transition), the temperature range is extended to above 1000℃, and there is no obvious phase separation in long-term cycling.

[0031] 2) Optimize oxygen ion conductivity, the ionic radius of Sc 3+ is closer to that of Zr 4+ , which can reduce lattice distortion and improve conductivity in the temperature range from room temperature to 800℃.

[0032] 3) Reduce aging effect, double-doping reduces grain boundary segregation at high temperature, thereby prolonging the service life of the electrolyte (experimental data show that the conductivity attenuation is less than 5% after 1000h aging at 1000℃).

[0033] (2) Nano-Al2O3 composite enhances mechanical properties Grain refinement: Al2O3 as a second phase particle is uniformly dispersed in the ZrO2 matrix, inhibiting excessive grain growth, and the average grain size of the material is controlled at 0.5μm-2μm, which can reduce crack initiation.

[0034] Dispersion strengthening and thermal shock resistance: the hard characteristic of Al2O3 improves the fracture toughness of the electrolyte, which is suitable for high-temperature frequent start-stop working conditions (such as solid oxide fuel cell SOFC).

[0035] Ion transport assistance: Al2O3 can adsorb impurity ions (such as Si), reduce grain boundary resistance, and increase the conductivity of the composite electrolyte at 800℃.

[0036] (3) High-temperature sintering densification can promote the interface bonding of (Y, Sc) ZrO2 and Al2O3, forming a continuous grain boundary structure. The PVA binder provides a temporary bonding network, and controlling the heating / cooling rate can avoid microcracks caused by the difference in thermal expansion coefficient.

[0037] (4) Simple process The sintering temperature is reduced to 1400℃~1600℃ (the sintering temperature of the traditional mechanical mixing method is >1650℃, with high energy consumption and poor uniformity), which can overcome the dissolution and lattice stress problems of dual doping, and the process is simple and controllable.

[0038] In some optional embodiments of the present application, the sol-gel method includes the following steps: Yttrium oxide, zirconium oxide and scandium oxide are dissolved in water, a cross-linking agent and a solvent are added, and a sol is formed by constant temperature stirring; the sol is vacuum dried to obtain a precursor gel.

[0039] In some optional embodiments of the present application, the molar ratio of zirconium oxide, cross-linking agent, and solvent is (0.5-1.5):1:(1-3). More preferably, the molar ratio of zirconium oxide, cross-linking agent, and solvent is 0.9:1:1.

[0040] The crosslinking agent in this application can be at least one of citric acid, tartaric acid and oxalic acid, preferably citric acid. The three carboxylic acid groups (-COOH) and hydroxyl groups (-OH) of citric acid can react with Y 3+ Sc 3+ 、Zr 4+ Such metal ions form stable complexes (such as [Zr(C6H5O7)] - ), prevent the metal ions from hydrolyzing and forming precipitates prematurely, and ensure the uniformity of the precursor solution. The molar ratio of citric acid to metal ions needs to be controlled at (1.2~1.5):1. Too low will lead to insufficient complexation, and too high will result in excessive residual organic matter. At the same time, citric acid can also slow down the hydrolysis rate of metal alkoxides by adjusting the solution pH to 3-4 (through carboxylic acid dissociation), avoiding local rapid condensation to form large particles. During the drying process, citric acid molecules form a three-dimensional network structure through hydrogen bonds and condensation reactions, which can fix the distribution of metal ions and thus reduce component segregation. Therefore, citric acid materials are preferred in this application.

[0041] The solvent in this application can be at least one of glycerol, ethylene glycol, polyvinyl butyral, and 1,2-propylene glycol, with ethylene glycol being preferred. Ethylene glycol can act as a crosslinking accelerator, with the hydroxyl groups reacting with the carboxylic acid groups of citric acid to form a citric acid-ethylene glycol ester crosslinked network, enhancing the mechanical strength of the gel and preventing cracking upon drying. Competitive coordination can also be used to regulate the hydrolysis-polycondensation kinetics of the metal alkoxide and control the sol viscosity.

[0042] In some optional embodiments of the present application, the temperature for constant temperature stirring is 75-90℃, and the time for constant temperature stirring is 4-6h; the temperature for vacuum drying is 120-150℃, and the time for vacuum drying is 15-20h. When the temperature for constant temperature stirring is between 75-90℃, the hydrolysis-polycondensation balance can be adjusted, the three-dimensional network structure can be formed, and phase separation can be prevented to avoid Y / Sc element segregation. If the temperature is too low, the gelation time will be longer, and the formed gel structure will be looser; if the temperature is too high, local boiling will cause the porosity to greatly increase, which is not conducive to the formation of the precursor gel.

[0043] In preferred embodiments of the present application, the temperature for constant temperature stirring is 80℃, and the stirring time is 5h to form a gel. Then, the precursor gel is prepared by vacuum drying at 130℃ for 18h.

[0044] In some optional embodiments of the present application, the particle size of the alumina is 20-100nm, and the ultrasonic dispersion parameters include: power 100-300W, frequency 20-50kHz, and time 25-40min. The particle size of the alumina will affect the grain boundary pinning. If the particle size is less than 20nm, the surface energy of the grain will be too high to cause agglomeration. If the particle size is greater than 100nm, it will become a crack source, which will cause the risk of cracking. The ultrasonic power should not be too large, and local heating can cause the gel to be pre-sintered. The time should not be too long.

[0045] In some optional embodiments of the present application, the dried composite slurry in step S3 is prepared by vacuum drying at 100-120℃ for 15-24h.

[0046] In some optional embodiments of the present application, the pre-sintering temperature in step S3 is 600-800℃, the pre-sintering time is 2.5-4h, and the heating rate is 3-8℃ / min. The pre-sintering can remove the organic matter, stabilize the TGA weight loss rate, and form YSZ primary crystals. Therefore, the pre-sintering temperature should not be too large, otherwise it will cause premature densification to hinder the diffusion of Al2O3. The pre-sintering heating rate should not be too fast to avoid the embryo cracking caused by thermal stress.

[0047] In some optional embodiments of the present application, the sintering in step S3 includes: adding 4-6wt% binder, dry pressing the pre-sintered material to shape, and then sintering at 1400-1600℃ for 4.5-6h. The heating rate is 3-8℃ / min. The binder is polyvinyl alcohol aqueous solution (5wt%), and the dry pressing pressure is 10-20MPa.

[0048] During sintering, the binder can optimize rheology, stabilize the viscosity of the slurry, and also improve the strength of the green body; the content of the binder affects the forming strength, and insufficient content of the binder will result in low strength of the green body, and excessive content of the binder will hinder sintering densification. Sintering process affects grain growth and densification, which can make Al2O3 distribute along the grain boundary at high temperature to obtain the effect of grain boundary purification. Sintering temperature and time are also crucial, if the sintering temperature is higher than 1600℃, YSZ will react with Al2O3 to generate ZrAlO3 impurities. If the sintering temperature is not high enough or the time is not enough, it may result in more pores, thereby leading to the performance degradation of the composite electrolyte.

[0049] The above technical solutions of the present application will be described in detail below in conjunction with specific embodiments. The hydrate content of Sc(NO3)3xH2O in the following examples is calibrated according to the supplier.

[0050] Example 1 This embodiment provides a high-temperature and high-stability double-doped composite electrolyte (double-doped Y-Sc-ZrO2 / Al2O3), which contains 0.08 mol of Y2O3, 0.02 mol of Sc2O3, 0.9 mol of ZrO2, and 10 wt% of Al2O3.

[0051] It is prepared by the following method: S101, 30.64g of Y(NO3)3·6H2O, 6g of Sc(NO3)3·xH2O and 387.9g of Zr(NO3)4·5H2O are weighed respectively, dissolved in 800mL of deionized water, 288.3g of citric acid and 93.1g of ethylene glycol are added, and the mixture is stirred at 80℃ for 5h to form a sol, and then vacuum dried at 130℃ for 18h to obtain a precursor gel.

[0052] S102, 100g of the precursor gel is taken, 10g of Al2O3 nano-powder with a particle size of 50nm is added, 150mL of deionized water (solid content of 40wt%) is added, ultrasonic dispersion is carried out at 150W and 40kHz for 30min, and then a planetary ball mill is used to grind at a speed of 400rpm for 10h to obtain a composite slurry, and the ZrO2 ball slurry ratio is 5:1.

[0053] S103, the composite slurry is vacuum dried at 120℃ for 18h, and then ground and pre-sintered at 700℃ for 3h with a heating rate of 5℃ / min.

[0054] S104, after pre-sintering, 3wt% of PVA aqueous solution (5%) binder is added, and the circular piece is dry-pressed into a Φ20mm×1.5mm circular piece under a pressure of 15MPa, and then sintered at 1500℃ for 5h to obtain the product, with a heating rate of 5℃ / min.

[0055] The ion conductivity of the double-doped Y-Sc-ZrO2 / Al2O3 material obtained in Example 1 is 0.12 S / cm at 800℃, the strength is 220 MPa, the grain size is 1.2 μm, and the TEC is 10.0 x 10-6 / K. -6 K -1 , and the attenuation rate is 3.8%. (The test method is as in the experimental example) Example 2 This embodiment provides a high-temperature and high-stability double-doped composite electrolyte (double-doped Y-Sc-ZrO2 / Al2O3), which contains 0.06 mol of Y2O3, 0.03 mol of Sc2O3, 0.9 mol of ZrO2, and 15 wt% of Al2O3.

[0056] It is prepared by the following method: S201, Y(NO3)3·6H2O, Sc(NO3)3·xH2O and Zr(NO3)4·5H2O are weighed according to the molar ratio, mixed and dissolved in 800 mL of deionized water, 288.3 g of citric acid and 93.1 g of ethylene glycol are added, and the sol is formed by magnetic stirring at 80℃ for 5h, and then vacuum dried at 130℃ for 18h to obtain a precursor gel.

[0057] S202, take 100g of the precursor gel, add Al2O3 nano-powder with a particle size of 50nm, add 150mL of deionized water, ultrasonic dispersion for 30min at 150W and 40kHz, and then use a planetary ball mill to grind for 10h at a speed of 400rpm to obtain a composite slurry, and the ZrO2 ball slurry ratio is 5:1.

[0058] S203, vacuum dry the composite slurry at 120℃ for 18h, grind and pre-sinter at 600℃ for 3h, and the heating rate is 5℃ / min.

[0059] S204, after pre-sintering, add 3wt% of PVA aqueous solution (5%) binder, dry press into Φ20mm x 1.5mm round sheet under a pressure of 15MPa, and then sinter the round sheet at 1450℃ for 6h to obtain the product, and the heating rate is 5℃ / min.

[0060] The ion conductivity of the double-doped Y-Sc-ZrO2 / Al2O3 material obtained in Example 2 is 0.10 S / cm at 800℃, the strength is 230 MPa, the grain size is 0.9 μm, and the TEC is 9.9 x 10-6 / K. -6 K -1 , and the attenuation rate is 4.2%. (The test method is as in the experimental example) Example 3 The embodiment provides a high-temperature and high-stability double-doped composite electrolyte (double-doped Y-Sc-ZrO2 / Al2O3), which contains 0.1 mol of Y2O3, 0.01 mol of Sc2O3, 0.9 mol of ZrO2 and 5 wt% of Al2O3.

[0061] The double-doped Y-Sc-ZrO2 / Al2O3 is prepared by the following method: S301, Y(NO3)3·6H2O, Sc(NO3)3·xH2O and Zr(NO3)4·5H2O are weighed according to the molar ratio, mixed and dissolved in 800 mL of deionized water, 288.3 g of citric acid and 93.1 g of ethylene glycol are added, and the sol is formed by magnetic stirring at 80 DEG C for 5 h, and then the precursor gel is prepared by vacuum drying at 130 DEG C for 18 h.

[0062] S302, 100 g of the precursor gel is taken, Al2O3 nano-powder with a particle size of 100 nm is added, 150 mL of deionized water is added, ultrasonic dispersion is carried out at 150 W and 40 kHz for 30 min, and then a planetary ball mill is used to grind at a speed of 400 rpm for 10 h to obtain a composite slurry, and the ZrO2 ball slurry ratio is 5:1.

[0063] S303, the composite slurry is vacuum dried at 120 DEG C for 18 h, and then ground and pre-sintered at 800 DEG C for 3 h, and the heating rate is 5 DEG C / min.

[0064] S304, after pre-sintering, 3 wt% of PVA aqueous solution (5%) binder is added, and the circular sheet with a diameter of 20 mm and a thickness of 1.5 mm is dry-pressed under a pressure of 15 MPa, and then the circular sheet is sintered at 1400 DEG C for 5 h to obtain the double-doped Y-Sc-ZrO2 / Al2O3 material, and the heating rate is 5 DEG C / min.

[0065] The double-doped Y-Sc-ZrO2 / Al2O3 material obtained in Example 3 has an ion conductivity of 0.11 S / cm at 800 DEG C, a strength of 210 MPa, a grain size of 1.5 μm, a TEC of 10.2*10 -6 K -1 , and an attenuation rate of 3.5% (the test method is as shown in the experimental example). Comparative Example 1 The difference between the comparative example and Example 1 is that the prepared composite electrolyte material (named Y-ZrO2 / Al2O3) is single yttria doped and combined with an alumina composite phase.

[0066] The double-doped Y-Sc-ZrO2 / Al2O3 is prepared by the following method: S1011, 38.3 g of Y(NO3)3·6H2O (0.1 mol Y2O3) and 383.6 g of Zr(NO3)4·5H2O were weighed and dissolved in 800 mL of deionized water, 288.3 g of citric acid and 93.1 g of ethylene glycol were added, and a sol was formed by magnetic stirring at 80°C for 5 h. The precursor gel was prepared by vacuum drying at 130°C for 18 h.

[0067] The remaining steps were the same as in Example 1.

[0068] Comparative Example 2 The difference between this comparative example and Example 1 is that the composite electrolyte material prepared (named Sc-ZrO2 / Al2O3) is a single scandium oxide doped with an alumina composite phase.

[0069] It was prepared by the following method: S1012, 15 g of Sc(NO3)3·xH2O (0.1 mol Sc2O3) and 383.6 g of Zr(NO3)4·5H2O were weighed and dissolved in 800 mL of deionized water, 288.3 g of citric acid and 93.1 g of ethylene glycol were added, and a sol was formed by magnetic stirring at 80°C for 5 h. The precursor gel was prepared by vacuum drying at 130°C for 18 h.

[0070] The remaining steps were the same as in Example 1.

[0071] Comparative Example 3 The difference between this comparative example and Example 1 is that the powders of yttrium oxide (Y2O3) and zirconium oxide (ZrO2) were mixed in a solid phase method at a molar ratio of 8%, and a composite electrolyte material was prepared by sintering at 1500°C for 5 h, named 8YSZ.

[0072] Experimental Example: 1. Ion conductivity: tested by AC impedance method, parameters: Zahner IM6, Pt electrode, 0.1 Hz~1 MHz, 800°C; 2. Flexural strength: tested by three-point bending method, parameters: Instron 5566, sample size: 3 mm x 4 mm x 36 mm, span: 30 mm, loading rate: 0.5 mm / min; 3. High temperature stability: 1000°C for 1000 h in a tube furnace, conductivity was tested every 200 h; 4. Thermal expansion coefficient (hereinafter referred to as TEC): expansion instrument Netzsch DIL 402C, Φ6 mm x 25 mm, 5°C / min, 25°C~1000°C; 5. Microstructure: SEM, scanning electron microscope (FEI Quanta 250), 10 kV.

[0073] The composite electrolyte materials prepared in Example 1 and Comparative Examples 1-3 were tested by the above method, and the results are shown in Table 1 and Figures 2-5 .

[0074] Table 1

[0075] As can be seen from Table 1, the double-doped material prepared in Example 1 is superior to the single-doped material in terms of conductivity and stability, overcoming the high cost and phase change problem of Sc single-doped material, and at the same time improving the defect of insufficient conductivity of Y single-doped material. And by precisely controlling the uniform distribution of Y and Sc through sol-gel method, the technical difficulties of solubility and lattice stress are solved.

[0076] Figure 2 The comparison curve of ion conductivity is shown in Figure 2 As can be seen from the comparison curve of ion conductivity, the initial conductivity increases with temperature, and when the temperature increases to 1000℃, the conductivity of the high-temperature and high-stability double-doped composite electrolyte prepared in Example 1 increases from 0.0196S / cm (600℃) to 0.207S / cm; while the conductivity of 8YSZ prepared in Comparative Example 3 increases from 0.0078S / cm (600℃) to 0.1S / cm. It shows that the conductivity of the high-temperature and high-stability double-doped composite electrolyte material prepared in the application is significantly higher than that of 8YSZ.

[0077] Figure 3 The comparison curve of thermal expansion coefficient is shown in Figure 3 As can be seen from the comparison curve of thermal expansion coefficient, the thermal expansion coefficient of 8YSZ prepared in Comparative Example 3 increases from 10.3×10 -6 K -1 (25℃) to 10.8×10 -6 K -1 (1000℃), the thermal expansion coefficient of Y-Sc-ZrO2 / Al2O3 prepared in Example 1 increases from 9.8×10 -6 K -1 (25℃) to 10.2×10 -6 K -1 (1000℃), which shows that the thermal expansion coefficient of Y-Sc-ZrO2 / Al2O3 of Example 1 of the application is slightly lower than that of 8YSZ, which further reflects the inhibitory effect of Al2O3.

[0078] Figure 4The microstructure of Y-Sc-ZrO2 / Al2O3 is shown in the figure, wherein the rectangular nodes represent ZrO2 matrix grains (0.5 μm-2 μm) and Y-Sc-ZrO2 structure formed by double doping (Y2O36 mol%-10 mol%, Sc2O31 mol%-3 mol%); the circular nodes represent Al2O3 nanoparticles (20 nm-100 nm) uniformly dispersed in the matrix; the arrow marks the pinning effect and grain growth inhibition function of Al2O3, and finally a dense microstructure is formed. Figure 4 The microstructure of the material and the functional relationship are briefly shown.

[0079] Figure 5 As shown in the curve of ion conductivity changing with time, the ion conductivity of Y-Sc-ZrO2 / Al2O3 prepared in the embodiment of the application attenuates from 0.207 S / cm to 0.199 S / cm (3.8%), the ion conductivity of Y-ZrO2 / Al2O3 (10Y) prepared in Comparative Example 1 attenuates from 0.083 S / cm to 0.076 S / cm (8.5%), the ion conductivity of Sc-ZrO2 / Al2O3 (10Sc) prepared in Comparative Example 2 attenuates from 0.264 S / cm to 0.237 S / cm (10.2%), and the ion conductivity of conventional 8YSZ prepared in Comparative Example 3 attenuates from 0.0595 S / cm to 0.052 S / cm (12.5%). It can be illustrated that the high-temperature and high-stability double-doped composite electrolyte material of the application attenuates most slowly with time at 1000°C, and the stability is significantly better than that of single-doped and 8YSZ.

[0080] Figure 6 The curve of mechanical strength changing with temperature is shown in the figure, and the temperature changes from 25°C to 1000°C. Figure 6 As shown in the figure, the mechanical strength of the high-temperature and high-stability double-doped composite electrolyte of the application decreases from 220 MPa to 200 MPa, the mechanical strength of Y-ZrO2 / Al2O3 (10Y) prepared in Comparative Example 1 decreases from 220 MPa to 180 MPa, the mechanical strength of Sc-ZrO2 / Al2O3 (10Sc) prepared in Comparative Example 2 decreases from 220 MPa to 150 MPa, and the mechanical strength of conventional 8YSZ prepared in Comparative Example 3 decreases from 220 MPa to 150 MPa. It is fully illustrated that the high-temperature and high-stability double-doped composite electrolyte material prepared in the embodiment of the application attenuates most slowly in strength at high temperature, and is better than single-doped and 8YSZ, and exhibits excellent strength retention capacity.

[0081] Although the specific embodiments of the application are described in detail, it should not be understood as limiting the protection scope of the patent. Various modifications and variations made by those skilled in the art within the scope described in the claims are still within the protection scope of the patent.

Claims

1. A high-temperature and high-stability dual-doped composite electrolyte, characterized in that: The composite phase comprises zirconia doped with yttria in an amount of 6 mol% to 10 mol%, zirconia doped with scandium oxide in an amount of 1 mol% to 3 mol%, and aluminum oxide in an amount of 5 wt% to 20 wt%.

2. The high-temperature and high-stability dual-doped composite electrolyte according to claim 1, characterized in that: The composite phase comprises 8 mol% yttria-doped zirconium oxide, 2 mol% scandium oxide-doped zirconium oxide and 10 wt% aluminum oxide.

3. A method for preparing a high-temperature and high-stability dual-doped composite electrolyte according to claim 1 or 2, characterized in that: The following steps are involved: Yttrium oxide, zirconium oxide, scandium oxide and aluminum oxide are mixed in proportion, and nitrate is used as a raw material to prepare a precursor gel by a sol-gel method; Alumina is added to the precursor gel, and then water is added, followed by ultrasonic dispersion and ball milling to obtain a composite slurry; The dried composite slurry is pre-sintered and sintered in sequence to obtain a high-temperature and high-stability dual-doped composite electrolyte.

4. The method for preparing a high-temperature and high-stability dual-doped composite electrolyte according to claim 3, characterized in that: The sol-gel method comprises the following steps: The nitrate of yttrium oxide, the nitrate of zirconium oxide and the nitrate of scandium oxide are dissolved in water, a cross-linking agent and a solvent are added, and the mixture is stirred at a constant temperature to form a sol; the sol is vacuum dried to obtain a precursor gel.

5. The method for preparing a high-temperature and high-stability dual-doped composite electrolyte according to claim 4, characterized in that: The molar ratio of zirconium oxide, cross-linking agent and solvent in the sol is (0.5-1.5):1:(1-3).

6. The method for preparing a high-temperature and high-stability dual-doped composite electrolyte according to claim 4, characterized in that: The constant temperature stirring temperature is 75° C. to 90° C., and the constant temperature stirring time is 4 h to 6 h; the vacuum drying temperature is 120° C. to 150° C., and the vacuum drying time is 15 h to 20 h.

7. The method for preparing a high-temperature and high-stability dual-doped composite electrolyte according to claim 3, characterized in that: The particle size of the aluminum oxide is 20 nm to 100 nm, and the parameters of the ultrasonic dispersion include: power of 100 W to 300 W, frequency of 20 kHz to 50 kHz, and time of 25 min to 40 min.

8. The method for preparing a high-temperature and high-stability dual-doped composite electrolyte according to claim 3, characterized in that: The dried composite slurry is prepared by vacuum drying at 100° C. to 120° C. for 15 h to 24 h.

9. The method for preparing a high-temperature and high-stability dual-doped composite electrolyte according to claim 3, characterized in that: The pre-sintering temperature is 600° C. to 800° C., the pre-sintering time is 2.5 h to 4 h, and the heating rate is 3° C. / min to 8° C. / min.

10. The method for preparing a high-temperature and high-stability dual-doped composite electrolyte according to claim 3, characterized in that: The sintering process includes: adding a binder, dry pressing the pre-sintered material to shape it, and then sintering it at 1400°C to 1600°C for 4.5 hours to 6 hours; The heating rate is 3℃ / min~8℃ / min; The binder is a 4wt%~6wt% polyvinyl alcohol aqueous solution, and the dry pressing pressure is 10MPa~20MPa.

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