A special crucible for sintering sodium battery cathode materials and its preparation method

Abstract

The present invention discloses a special crucible for sintering sodium battery cathode materials and a preparation method thereof. The preparation method comprises the following steps: S1. Mix a premixed granular material and a premixed fine powder in a certain mass ratio to obtain a mixed material, and add a certain amount of potassium hexafluorozirconate solution to the mixed material and stir to obtain a casting material; S2. Cast and vibrate the casting material to form, cure, and demold to obtain a green crucible blank; S3. After drying the green crucible blank for a period of time, perform high-temperature heat treatment for a period of time to obtain a special crucible for sintering sodium battery cathode materials; wherein, the premixed granular material comprises calcium hexaaluminate particles and electrofused zirconia corundum particles; the premixed fine powder comprises calcium hexaaluminate fine powder, calcium dialuminate fine powder, dodecacalcium heptaaluminate fine powder, calcium acetate fine powder, and rare earth composite yttrium zirconium ceramic powder. The process of the present invention is simple, and the prepared crucible has high density, high strength, strong anti-permeability, good anti-corrosion property, and high thermal shock stability.

Description

Technical Field

[0001] The present invention relates to the technical field of refractories, and particularly to a special crucible for sintering sodium battery cathode materials and a preparation method thereof. Background Art

[0002] Sodium-ion batteries are an important part of the new energy field, mainly composed of cathode materials, anode materials, electrolyte, separator, etc. Among them, the cathode material has the highest cost proportion and the greatest impact on battery performance ( Bai Xiaoyu, Guo Wen Lin, Ren Zhiqiang, et al. Latest progress in cathode materials for sodium-ion batteries [J]. Modern Chemical Industry, 2023, 43(4): 76-80 ).

[0003] According to different sodium battery cathodes, their preparation methods are different. Currently, sodium battery cathodes mainly include three categories: Prussian compounds, anion compounds, and layered transition metal oxides ( Zhu Zhanshu, Zhou Yu, Liu Jiefei, et al. Research progress in cathode materials for sodium-ion batteries [J]. Chinese Journal of Power Sources, 2023, 47(6): 715-720 ), among which layered transition metal oxides have attracted much attention due to their wide raw material sources, simple preparation process (high-temperature solid-state method), and suitability for large-scale industrial production.

[0004] In the process of preparing sodium battery cathode materials by high-temperature solid-state sintering process, the cathode precursor is placed in a crucible, cooled and separated after high-temperature calcination, and repeated. It can be seen that under the calcination conditions of sodium battery cathode materials, the crucible not only faces cyclic thermal stress damage, but also directly contacts with the strongly alkaline sodium battery cathode and suffers erosion, thus posing strict requirements on the service performance of the crucible.

[0005] Currently, due to the high technical barriers and technical confidentiality of sodium battery cathodes, there are few reports on the crucibles used in their high-temperature preparation process. Most of them are explored by referring to the crucibles for high-temperature solid-state sintering of lithium battery cathodes, but the service effects are very different, which are specifically manifested in the following aspects:

[0006] (1) The erosion of sodium battery cathodes is stronger. The cathode precursor of sodium battery mainly uses sodium carbonate as raw material. Due to the larger sodium ion radius and stronger alkalinity, the severity of the erosion reaction on the crucible is also higher. The cordierite-mullite / spinel crucible used for sintering lithium battery cathodes in the past can hardly resist the erosion of sodium battery cathodes. The main reason is that the lithium-aluminum-silicon compounds (such as β-eucryptite, etc.) formed by the reaction of aluminum-silicon components in the cordierite-mullite / spinel crucible with lithium-containing components are low-expansion glass phases, while the sodium-aluminum-silicon compounds (such as nepheline, etc.) formed by the reaction of aluminum-silicon components with sodium-containing components are high-expansion phases, directly leading to the cracking and damage of the crucible.

[0007] (2) The influence of the forming process. Traditional crucibles mainly use semi-dry mechanical pressing for forming, and the main drawback of this process is that the porosity of the products is relatively high, generally about 22% - 29%. Under the erosion of highly permeable sodium battery cathodes, the service performance of the crucible cannot be guaranteed.

[0008] (3) Influence of the amount of cathode material loaded in the sagger. The lithium sources (lithium carbonate or lithium hydroxide) used in the lithium-ion battery cathode precursor have a small density and low specific gravity because lithium itself has a small atomic number. In contrast, the density and specific gravity of the sodium sources (such as sodium carbonate) used in the sodium-ion battery cathode precursor are significantly higher than those of the lithium sources. Under the same volume condition (the loading capacity of the sagger remains unchanged), the amount of sodium-ion battery cathode loaded in the sagger is significantly more than that of the lithium-ion battery cathode, which also causes more serious erosion of the sagger by the sodium-ion battery cathode.

[0009] The patented technology "A sagger for sintering sodium-ion battery cathode materials and its preparation method 202310218925.2" publicly reports that using magnesium aluminate spinel particles and magnesium aluminate spinel fine powder as raw materials, after preparing a mixed solution, aging with the mixture, then pressing into shape by machine, drying, and firing, a sagger for sintering sodium-ion battery cathode materials is obtained. This invention uses magnesium aluminate spinel with strong erosion resistance as the raw material to reduce the erosion reaction degree between the sagger and the sodium-ion battery cathode, and toughens by the in-situ formation of whiskers to improve the thermal shock resistance of the sagger. However, the semi-dry pressing process conditions determine that the sagger products have a low density (low bulk density) and a high apparent porosity, which cannot effectively resist the penetration of the sodium-ion battery cathode; in addition, under the erosion conditions of strong alkaline components in the sodium-ion battery cathode, there are also drawbacks of free MgO in spinel, weakening the anti-spalling performance of the sagger. Summary of the Invention

[0010] The purpose of the present invention is to propose a special sagger for sintering sodium-ion battery cathode materials and its preparation method in view of the above deficiencies of the prior art. The process of this method is simple, and the prepared sagger has a high density, high strength, strong anti-permeability, good anti-erosion performance, and high thermal shock stability.

[0011] A preparation method of a special sagger for sintering sodium-ion battery cathode materials according to the present invention includes the following steps:

[0012] S1. Mix a premixed granular material and a premixed fine powder in a certain mass ratio to obtain a mixture, and add a certain amount of potassium fluozirconate solution to the mixture and stir to obtain a casting material;

[0013] S2. Cast and vibrate the casting material to form a shape, maintain, and demold to obtain a green body of the sagger;

[0014] S3. After drying the green body of the sagger for a certain period of time, perform high-temperature heat treatment for a certain period of time to obtain a special sagger for sintering sodium-ion battery cathode materials;

[0015] Among them, the premixed granular material includes calcium hexaaluminate particles and fused zirconia corundum particles; the premixed fine powder includes calcium hexaaluminate fine powder, calcium dialuminate fine powder, dodecacalcium heptaaluminate fine powder, calcium acetate fine powder, and rare earth composite yttrium zirconium ceramic powder.

[0016] Further, the mass ratio of the calcium hexaaluminate particles to the electrofused zircon corundum particles is 100:(15-35).

[0017] Further, the mass ratio of the calcium hexaaluminate fine powder: calcium dialuminate fine powder: dodecacalcium heptaaluminate fine powder: calcium acetate fine powder: rare earth composite yttrium zirconium ceramic powder is 100:(25-30):(10-15):(3.8-5.5):(2.8-4.4).

[0018] Further, the mass ratio of the premixed granular material to the premixed fine powder material is 100:(65-70).

[0019] Further, the potassium fluozirconate solution accounts for 6-8 wt% of the mixture, and the concentration of the potassium fluozirconate solution is 10-12 wt%.

[0020] Further, the specific operation of step S1 is as follows:

[0021] 1) Mix calcium hexaaluminate particles and electrofused zircon corundum particles with a certain mass ratio to obtain a premixed granular material;

[0022] 2) Mix calcium hexaaluminate fine powder, calcium dialuminate fine powder, dodecacalcium heptaaluminate fine powder, calcium acetate fine powder and rare earth composite yttrium zirconium ceramic powder with a certain mass ratio to obtain a premixed fine powder material;

[0023] 3) Mix a premixed granular material and a premixed fine powder material with a certain mass ratio to obtain a mixture;

[0024] 4) Add a certain amount of potassium fluozirconate solution to the mixture and stir to obtain a casting material.

[0025] Further, in step S3, the green body of the sagger is dried at 100-110 °C for 8-10 hours, then placed in a tunnel kiln and fired at 1220-1280 °C for 2-5 hours of heat preservation, and cooled to room temperature to obtain a special sagger for sintering sodium battery positive electrode materials.

[0026] Further, the particle size of the calcium hexaaluminate particles is 2-4 mm, and the particle size shows a continuous distribution, where the mass ratio of the particles in the range of [2 mm - 2.5 mm], (2.5 mm - 3 mm], (3 mm - 3.5 mm] and (3.5 mm - 4 mm] is (25-30):(25-30):(15-20):(15-20).

[0027] Further, the particle size of the electrofused zircon corundum particles is 1-3 mm, and the particle size shows a discontinuous distribution, where the mass ratio of the particles in the range of [1 mm - 1.4 mm] and [2.8 mm - 3 mm] is (60-65):(30-35);

[0028] The chemical composition of the electrofused zircon corundum particles is that the Al2O3 content is 90-94 wt%, and the ZrO2 content is ≥5 wt%.

[0029] The particle size of the calcium hexaaluminate fine powder is 70-80 μm.

[0030] The particle size of the calcium dialuminate fine powder is 55-60 μm.

[0031] The particle size of the dodecacalcium heptaaluminate fine powder is 45-50 μm; the particle size of the calcium acetate fine powder is 25-30 μm.

[0032] A special crucible for sintering sodium battery cathodes prepared by the above preparation method.

[0033] The beneficial effects of the present invention are as follows:

[0034] (1) The present invention adopts the casting vibration molding process to avoid segregation under the semi-dry mechanical pressing molding process. Through the uniform dispersion in the solid-liquid mixing system of the mixture and the close combination of the aggregate and fine powder, the apparent porosity of the crucible is reduced, the density of the crucible is increased, the mechanical strength of the crucible is increased, and the penetration of the sodium battery cathode is reduced.

[0035] (2) The present invention selects non-free calcium-containing component refractory raw materials, which have high alkalinity, high temperature resistance, and non-hydration. Combining with the large lattice voids of the calcium aluminate-based compounds, a solid solution sintering is formed in-situ with the zircon corundum component at high temperature, enhancing the overall bonding performance of the crucible and improving the alkali erosion resistance of the crucible.

[0036] (3) The present invention utilizes the "laminated" structure formed by the plate-like crystals of calcium hexaaluminate during the firing process to effectively improve the anti-permeability performance of the crucible; at the same time, under the erosion of the sodium battery cathode, the eutectic combination of sodium aluminate and precipitated corundum formed by the desolution of calcium hexaaluminate improves the bonding strength and density under the service conditions of the crucible, avoids cracking and spalling of the crucible during the erosion process, and further reduces the penetration of the sodium battery cathode into the crucible while improving the anti-spalling property of the crucible.

[0037] (4) The present invention adjusts the gradation of the particle composition, and constructs multi-scale pores by the continuous and discontinuous stacking of aggregate particles, realizing the uniform distribution of the pore structure of the crucible, which is beneficial to improving the thermal shock resistance of the crucible. Combining with the non-wetting property and high-temperature phase change toughening effect of the rare earth composite powder, the thermal shock resistance of the crucible is further improved.

[0038] (5) The present invention utilizes the ionization of potassium hexafluorozirconate solution to form [ZrF6] 2- ion coating and bonding, providing the early strength of the green crucible; during the high-temperature firing process, the in-situ decomposition of calcium acetate forms micro-pores and highly active micro-crystals, which are solid-solution combined with zirconium-containing groups, improving the sintering performance of the crucible, reducing the sintering temperature of the crucible, and saving energy and resources.

[0039] The special sagger for sintering sodium positive electrode materials prepared by the present invention has been tested:

[0040] Apparent porosity 11-13% (GB / T2997-2015);

[0041] Flexural strength 22~26MPa (GB / T3001-2017);

[0042] The residual flexural strength retention rate of the thermal shock stability test (GB / T30873-2014) after 5 times of 1100℃ circulating water cooling is 94-95%, and the strength change rate of the alkali resistance test (GB / T14983-2008) after 1100℃×30h is 3.2-3.7%.

[0043] Therefore, the process of the present invention is simple, and the prepared sagger has high density, high strength, strong anti-permeability, good erosion resistance and high thermal shock stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a SEM photograph of the special sintering sagger sample for sodium cathode material prepared in Example 1.

[0045] Figure 2 This is a photograph of the appearance of the sagger sample for sintering sodium cathode materials prepared in Example 1 after corrosion. DETAILED DESCRIPTION

[0046] The following are specific embodiments of the present invention and the accompanying drawings to further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments.

[0047] Example 1

[0048] A method for preparing a special sagger for sintering sodium cathode materials, the specific steps are as follows:

[0049] 1) Calcium hexaaluminate particles and fused zirconium corundum particles were prepared in a mass ratio of 100:35 and added to a blender and mixed for 10 minutes to obtain a premixed granular material;

[0050] 2) Calcium hexaaluminate fine powder: calcium dialuminate fine powder: calcium dodecaluminate fine powder: calcium acetate fine powder: rare earth composite yttrium zirconium ceramic powder were prepared in a mass ratio of 100:30:10:3.8:4.4, added to a roller mixer and mixed for 35 minutes to obtain a premixed fine powder;

[0051] 3) The premixed granules and premixed fine powder were prepared in a mass ratio of 100:70, added to a blender and mixed for 12 minutes to obtain a mixture;

[0052] 4) adding a potassium fluorozirconate solution accounting for 7 wt % of the mixture to the mixture, stirring for 6 minutes, placing the mixture in a mold, casting and vibrating the mixture, curing at 28° C. for 2 hours, and demolding to obtain a sagger green body;

[0053] 5) After the sagger green body is dried at 110° C. for 9 hours, it is placed in a tunnel kiln and sintered at 1270° C. for 4 hours, and cooled to room temperature to obtain a sagger specifically for sintering sodium cathode materials.

[0054] The particle size of calcium hexaaluminate is 2 to 4 mm, and the particle size is continuously distributed, wherein the mass ratio of [2 mm to 2.5 mm] particles, (2.5 mm to 3 mm] particles, (3 mm to 3.5 mm] particles and (3.5 mm to 4 mm] particles is 30:30:20:20.

[0055] The particle size of fused zirconium corundum is 1 to 3 mm, and the particle size is discontinuously distributed, among which the mass ratio of [1 mm to 1.4 mm] particles to [2.8 mm to 3 mm] particles is 65:35;

[0056] The chemical composition of the fused zirconium corundum particles is 92wt% Al2O3 and 7wt% ZrO2;

[0057] The particle size of calcium hexaaluminate fine powder is 70-80 μm;

[0058] The particle size of calcium dialuminate fine powder is 55-60 μm;

[0059] The particle size of the fine powder of dodecacalcium heptaaluminate is 45 to 50 μm; the particle size of the fine powder of calcium acetate is 25 to 30 μm.

[0060] The concentration of the potassium fluorozirconate solution was 10 wt%.

[0061] The product brand of rare earth composite yttrium zirconium ceramic powder is YZ5.25QLC, refer to GB / T31968-2015.

[0062] Figure 1 This is an SEM image of a sample from a sagger used for sintering sodium cathode materials. It shows a tight internal bond and a complete overall structure. Matrix fine powder is evenly dispersed around the aggregate particles, and the aggregate and matrix are tightly sintered, with no holes or through-cracks.

[0063] Figure 2 This is a photograph of a crucible sample used for sintering sodium cathode materials after being etched by a sodium cathode material precursor. As can be seen, the crucible remains intact, with no signs of cracking or shedding; the sidewalls are free of adhesion or flaking; and the bottom of the crucible exhibits no peeling or delamination, demonstrating the sample's excellent overall structure and corrosion resistance at high temperatures.

[0064] The special sagger for sintering the sodium cathode material prepared in this embodiment was tested:

[0065] Apparent porosity 12% (GB / T2997-2015);

[0066] Flexural strength 22MPa (GB / T3001-2017);

[0067] The residual flexural strength retention rate of the thermal shock stability test (GB / T30873-2014) after 5 times of 1100℃ circulating water cooling is 94.4%, and the strength change rate of the alkali resistance test (GB / T14983-2008) after 1100℃×30h is 3.6%.

[0068] Example 2

[0069] A method for preparing a special sagger for sintering sodium cathode materials, the specific steps are as follows:

[0070] 1) Calcium hexaaluminate particles and fused zirconium corundum particles were prepared in a mass ratio of 100:25 and added to a blender and mixed for 11 minutes to obtain a premixed granular material;

[0071] 2) Calcium hexaaluminate fine powder: calcium dialuminate fine powder: calcium dodecaluminate fine powder: calcium acetate fine powder: rare earth composite yttrium zirconium ceramic powder were prepared in a mass ratio of 100:27:12:4.2:3.6 and added to a roller mixer and mixed for 36 minutes to obtain a premixed fine powder;

[0072] 3) The premixed granules and premixed fine powder were mixed in a blender at a mass ratio of 100:66, and mixed for 13 minutes to obtain a mixture;

[0073] 4) adding a potassium fluorozirconate solution accounting for 6 wt% of the mixture to the mixture, stirring for 5 minutes, placing the mixture in a mold, casting and vibrating the mixture, curing at 25° C. for 3 hours, and demolding to obtain a sagger green body;

[0074] 5) After the sagger green body is dried at 105° C. for 8 hours, it is placed in a tunnel kiln and fired at 1280° C. for 5 hours, and cooled to room temperature to obtain a sagger specifically for sintering sodium cathode materials.

[0075] The particle size of calcium hexaaluminate is 2 to 4 mm, and the particle size is continuously distributed, wherein the mass ratio of [2 mm to 2.5 mm] particles, (2.5 mm to 3 mm] particles, (3 mm to 3.5 mm] particles and (3.5 mm to 4 mm] particles is 28:25:15:15.

[0076] The particle size of fused zirconium corundum is 1 to 3 mm, and the particle size is discontinuously distributed, among which the mass ratio of [1 mm to 1.4 mm] particles to [2.8 mm to 3 mm] particles is 63:32;

[0077] The chemical composition of the fused zirconium corundum particles is 94wt% Al2O3 and 5wt% ZrO2;

[0078] The particle size of calcium hexaaluminate fine powder is 70-80 μm;

[0079] The particle size of calcium dialuminate fine powder is 55-60 μm;

[0080] The particle size of the fine powder of dodecacalcium heptaaluminate is 45 to 50 μm; the particle size of the fine powder of calcium acetate is 25 to 30 μm.

[0081] The concentration of the potassium fluorozirconate solution was 12 wt %.

[0082] The product brand of rare earth composite yttrium zirconium ceramic powder is YZ5.25QLC, refer to GB / T31968-2015.

[0083] The special sagger for sintering the sodium cathode material prepared in this embodiment was tested:

[0084] Apparent porosity 13% (GB / T2997-2015);

[0085] Flexural strength 24MPa (GB / T3001-2017);

[0086] The residual flexural strength retention rate of the thermal shock stability test (GB / T30873-2014) after 5 times of 1100℃ circulating water cooling is 94%, and the strength change rate of the alkali resistance test (GB / T14983-2008) after 1100℃×30h is 3.7%.

[0087] Example 3

[0088] A method for preparing a special sagger for sintering sodium cathode materials, the specific steps are as follows:

[0089] 1) Calcium hexaaluminate particles and fused zirconium corundum particles were prepared in a mass ratio of 100:30 and added to a blender and mixed for 10 minutes to obtain a premixed granular material;

[0090] 2) Calcium hexaaluminate fine powder: calcium dialuminate fine powder: calcium dodecaluminate fine powder: calcium acetate fine powder: rare earth composite yttrium zirconium ceramic powder were prepared in a mass ratio of 100:29:11:4.7:3.8, added to a roller mixer and mixed for 38 minutes to obtain a premixed fine powder;

[0091] 3) The premixed granules and premixed fine powder were mixed in a blender at a mass ratio of 100:68, and mixed for 12 minutes to obtain a mixture;

[0092] 4) Add potassium hexafluorozirconate solution accounting for 7 wt% of the mixture. After stirring for 6 minutes, pour it into a mold and vibrate it to form. Cure it for 2 hours at 30 °C, then demold to obtain the green body of the sagger.

[0093] 5) Dry the green body of the sagger at 100 °C for 9 hours, then place it in a tunnel kiln and keep it at 1250 °C for 3 hours for firing. Cool it to room temperature to obtain the special sagger for sintering sodium battery positive electrode materials.

[0094] Among them, the particle size of calcium hexaaluminate particles is 2 - 4 mm, and the particle size shows a continuous distribution. The mass ratio of [2 mm - 2.5 mm] particles, (2.5 mm - 3 mm] particles, (3 mm - 3.5 mm] and (3.5 mm - 4 mm] particles is 30:25:15:18.

[0095] The particle size of fused zirconia corundum particles is 1 - 3 mm, and the particle size shows an intermittent distribution. The mass ratio of [1 mm - 1.4 mm] particles and [2.8 mm - 3 mm] particles is 65:30.

[0096] The chemical composition of the fused zirconia corundum particles is 93 wt% of Al2O3 content and 5 wt% of ZrO2 content.

[0097] The particle size of calcium hexaaluminate fine powder is 70 - 80 μm.

[0098] The particle size of calcium dialuminate fine powder is 55 - 60 μm.

[0099] The particle size of dodecacalcium heptaaluminate fine powder is 45 - 50 μm; the particle size of calcium acetate fine powder is 25 - 30 μm.

[0100] The concentration of the potassium hexafluorozirconate solution is 10 wt%.

[0101] The product grade of the rare earth composite yttrium zirconium ceramic powder is YZ5.25QLC, see GB / T31968—2015.

[0102] The special sagger for sintering sodium battery positive electrode materials prepared in this example is tested:

[0103] The apparent porosity is 12% (GB / T2997 - 2015);

[0104] The flexural strength is 25 MPa (GB / T3001 - 2017);

[0105] The residual flexural strength retention rate of the 5 - cycle water - cooling thermal shock stability test at 1100 °C (GB / T30873 - 2014) is 94.1%, and the strength change rate of the 1100 °C × 30 h alkali - resistance test (GB / T14983 - 2008) is 3.3%.

[0106] Example 4

[0107] A method for preparing a special sagger for sintering sodium cathode materials, the specific steps are as follows:

[0108] 1) Calcium hexaaluminate particles and fused zirconium corundum particles were prepared in a mass ratio of 100:15 and added to a blender and mixed for 12 minutes to obtain a premixed granular material;

[0109] 2) Calcium hexaaluminate fine powder: calcium dialuminate fine powder: calcium dodecaluminate fine powder: calcium acetate fine powder: rare earth composite yttrium zirconium ceramic powder were prepared in a mass ratio of 100:25:15:5.5:2.8, added to a roller mixer and mixed for 40 minutes to obtain a premixed fine powder;

[0110] 3) The premixed granules and premixed fine powder were mixed in a blender at a mass ratio of 100:65, and mixed for 15 minutes to obtain a mixture;

[0111] 4) adding 8 wt% of potassium fluorozirconate solution to the mixture, stirring for 8 minutes, placing the mixture in a mold, casting and vibrating, curing at 30° C. for 3 hours, and demolding to obtain a sagger green body;

[0112] 5) After the sagger green body is dried at 100° C. for 10 hours, it is placed in a tunnel kiln and sintered at 1220° C. for 2 hours, and cooled to room temperature to obtain a sagger specifically for sintering sodium cathode materials.

[0113] The particle size of calcium hexaaluminate is 2 to 4 mm, and the particle size is continuously distributed, wherein the mass ratio of [2 mm to 2.5 mm] particles, (2.5 mm to 3 mm] particles, (3 mm to 3.5 mm] particles and (3.5 mm to 4 mm] particles is 25:25:20:20.

[0114] The particle size of fused zirconium corundum is 1 to 3 mm, and the particle size is discontinuously distributed, among which the mass ratio of [1 mm to 1.4 mm] particles to [2.8 mm to 3 mm] particles is 2:1;

[0115] The chemical composition of the fused zirconium corundum particles is 90wt% Al2O3 and 8wt% ZrO2;

[0116] The particle size of calcium hexaaluminate fine powder is 70-80 μm;

[0117] The particle size of calcium dialuminate fine powder is 55-60 μm;

[0118] The particle size of the fine powder of dodecacalcium heptaaluminate is 45 to 50 μm; the particle size of the fine powder of calcium acetate is 25 to 30 μm.

[0119] The concentration of the potassium fluorozirconate solution was 11 wt %.

[0120] The product brand of rare earth composite yttrium zirconium ceramic powder is YZ5.25QLC, refer to GB / T31968-2015.

[0121] The special sagger for sintering the sodium cathode material prepared in this embodiment was tested:

[0122] Apparent porosity 11% (GB / T2997-2015);

[0123] Flexural strength 26MPa (GB / T3001-2017);

[0124] The residual flexural strength retention rate of the thermal shock stability test (GB / T30873-2014) after 5 times of 1100℃ circulating water cooling is 95%, and the strength change rate of the alkali resistance test (GB / T14983-2008) after 1100℃×30h is 3.2%.

[0125] Comparative Example 1

[0126] A method for preparing a sagger for sintering sodium cathode materials, comprising the following steps:

[0127] 1) Calcium hexaaluminate particles and fused zirconium corundum particles were prepared in a mass ratio of 100:70 and added to a blender and mixed for 11 minutes to obtain a premixed granular material;

[0128] 2) Calcium hexaaluminate fine powder: calcium dialuminate fine powder: calcium dodecaluminate fine powder: calcium acetate fine powder: rare earth composite yttrium zirconium ceramic powder were prepared in a mass ratio of 100:27:12:4.2:3.6 and added to a roller mixer and mixed for 36 minutes to obtain a premixed fine powder;

[0129] 3) The premixed granules and premixed fine powder were prepared in a mass ratio of 100:66, added to a blender and mixed for 13 minutes to obtain a mixture;

[0130] 4) adding a potassium fluorozirconate solution accounting for 6 wt% of the mixture to the mixture, stirring for 5 minutes, placing the mixture in a mold, casting and vibrating the mixture, curing at 25° C. for 3 hours, and demolding to obtain a sagger green body;

[0131] 5) After the sagger green body is dried at 105° C. for 8 hours, it is placed in a tunnel kiln and sintered at 1280° C. for 5 hours, and cooled to room temperature to obtain a sagger for sintering sodium positive electrode materials.

[0132] The particle size of calcium hexaaluminate is 2 to 4 mm, and the particle size is continuously distributed, wherein the mass ratio of [2 mm to 2.5 mm] particles, (2.5 mm to 3 mm] particles, (3 mm to 3.5 mm] particles and (3.5 mm to 4 mm] particles is 10:5:80:5.

[0133] The particle size of fused zirconia corundum grains is 1 - 3 mm, and the particle size shows a discontinuous distribution. The mass ratio of [1 mm - 1.4 mm] grains to [2.8 mm - 3 mm] grains is 1:9;

[0134] The chemical composition of the fused zirconia corundum grains is 94 wt% of Al2O3 content and 5 wt% of ZrO2 content;

[0135] The particle size of calcium hexaaluminate fine powder is 70 - 80 μm;

[0136] The particle size of calcium dialuminate fine powder is 55 - 60 μm;

[0137] The particle size of dodecacalcium heptaaluminate fine powder is 45 - 50 μm; the particle size of calcium acetate fine powder is 25 - 30 μm.

[0138] The concentration of potassium zirconium fluoride solution is 12 wt%.

[0139] The product grade of rare earth composite yttrium zirconium ceramic powder is YZ5.25QLC, see GB / T31968—2015.

[0140] The saggers for sintering sodium - ion battery positive electrode materials prepared in this comparative example were tested:

[0141] The apparent porosity is 18% (GB / T2997 - 2015);

[0142] The flexural strength is 14 MPa (GB / T3001 - 2017);

[0143] The residual flexural strength retention rate in the 5 - cycle water - cooling thermal shock stability test at 1100 °C (GB / T30873 - 2014) is 81%, and the strength change rate in the alkali - resistance test at 1100 °C × 30 h (GB / T14983 - 2008) is 6.8%.

[0144] It can be seen that by changing the ratio of calcium hexaaluminate grains to fused zirconia corundum grains, increasing the content of fused zirconia corundum grains, and at the same time adjusting the composition ratio of their particle sizes, the packing morphology of calcium hexaaluminate and fused zirconia corundum grains is changed. Since the specific gravity of fused zirconia corundum is greater than that of calcium hexaaluminate, the packing between particles is more likely to segregate, resulting in uneven primary pore structure, thereby reducing the sintering performance of the sagger, increasing the apparent porosity of the sagger, and at the same time reducing its mechanical strength. Under the influence of uneven pore distribution, the thermal shock stability of the sagger is weakened, and the strength change rate in the alkali - resistance test increases significantly.

[0145] For those not covered above, the prior art shall apply.

[0146] Although some specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are only for illustration and not for limiting the scope of the present invention. Those skilled in the technical field to which the present invention pertains can make various modifications or supplements to the described specific embodiments or use similar means for substitution, but will not deviate from the direction of the present invention or exceed the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc. made to the above embodiments based on the technical essence of the present invention should all be included within the protection scope of the present invention.

Claims

1. A method for preparing a special sagger for sintering sodium cathode materials, characterized in that: The steps include: S1. Mixing a premixed granular material and a premixed fine powder in a certain mass ratio to obtain a mixture, adding a certain amount of potassium fluorozirconate solution to the mixture and stirring to obtain a castable; S2, pouring the castable into a vibratory mold, curing, and demoulding to obtain a sagger green body; S3, drying the sagger green body for a period of time, and then heat treating it at a high temperature for a period of time to obtain a sagger specifically for sintering sodium cathode materials; The premixed granular material includes calcium hexaaluminate particles and fused zirconium corundum particles; the premixed fine powder material includes calcium hexaaluminate fine powder, calcium dialuminate fine powder, calcium dodecaaluminate fine powder, calcium acetate fine powder and rare earth composite yttrium zirconium ceramic powder; The mass ratio of the calcium hexaaluminate fine powder: the calcium dialuminate fine powder: the calcium dodecaluminate fine powder: the calcium acetate fine powder: the rare earth composite yttrium zirconium ceramic powder is 100: (25-30): (10-15): (3.8-5.5): (2.8-4.4); The calcium hexaaluminate particles have a particle size of 2-4 mm and are continuously distributed, wherein the mass ratio of [2 mm-2.5 mm] particles, [2.5 mm-3 mm] particles, [3 mm-3.5 mm] particles, and [3.5 mm-4 mm] particles is (25-30): (25-30): (15-20): (15-20); The fused zirconium corundum particles have a particle size of 1-3 mm and are discontinuously distributed, wherein the mass ratio of [1 mm-1.4 mm] particles to [2.8 mm-3 mm] particles is (60-65): (30-35).

2. The method for preparing a special sagger for sintering sodium cathode materials according to claim 1, characterized in that: The mass ratio of the calcium hexaaluminate particles to the fused zirconium corundum particles is 100:(15-35).

3. The method for preparing a special sagger for sintering sodium cathode materials according to claim 1 or 2, characterized in that: The mass ratio of the premixed granular material to the premixed fine powder is 100:(65-70).

4. The method for preparing a special sagger for sintering sodium cathode materials according to claim 1, characterized in that: The potassium fluorozirconate solution accounts for 6-8 wt % of the mixture, and the concentration of the potassium fluorozirconate solution is 10-12 wt %.

5. The method for preparing a special sagger for sintering sodium cathode materials according to claim 1, characterized in that: The specific operations of step S1 are as follows: 1) Mixing calcium hexaaluminate particles and fused zirconium corundum particles in a certain mass ratio to obtain premixed particles; 2) Mixing a certain mass ratio of calcium hexaaluminate fine powder, calcium dialuminate fine powder, calcium dodecaaluminate fine powder, calcium acetate fine powder and rare earth composite yttrium zirconium ceramic powder to obtain a premixed fine powder; 3) Mixing a certain mass ratio of premixed granular material and premixed fine powder to obtain a mixture; 4) Add a certain amount of potassium fluorozirconate solution to the mixture and stir to obtain a castable.

6. The method for preparing a special sagger for sintering sodium cathode materials according to claim 1, characterized in that: In step S3, the sagger green body is dried at 100-110° C. for 8-10 hours, then placed in a tunnel kiln and sintered at 1220-1280° C. for 2-5 hours, and cooled to room temperature to obtain a sagger specifically for sintering sodium cathode materials.

7. The method for preparing a special sagger for sintering sodium cathode materials according to claim 1, characterized in that: The chemical composition of the fused zirconium corundum particles is 90-94wt% Al2O3 and ≥5wt% ZrO2; The particle size of the calcium hexaaluminate fine powder is 70-80 μm; The particle size of the calcium dialluminate fine powder is 55-60 μm; The particle size of the dodecaluminate heptaaluminate fine powder is 45-50 μm; the particle size of the calcium acetate fine powder is 25-30 μm.

8. A special sagger for sintering sodium cathode materials prepared by the preparation method according to any one of claims 1 to 7.

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