Aluminum titanate composite saggar, preparation method and application thereof

Abstract

This invention belongs to the field of new energy battery technology, specifically a composite aluminum titanate crucible, its preparation method, and its application. The crucible comprises an inner working layer and an outer substrate layer. The inner layer is 1-3 mm thick and its raw materials include 20-80 parts synthetic aluminum titanate, 5-10 parts kaolin, 10-80 parts spinel, and 0-20 parts alumina. The outer layer raw materials include mullite, kaolin, alumina, cordierite, talc, and fused silica. The average coefficient of thermal expansion of the inner layer material from room temperature to 1000℃ is ≤2.0×10⁻⁶. ‑6 / K, outer layer = 3.0~5.0×10 ‑6 / K. The inner and outer layers are integrally pressed and sintered to form a gradient interface diffusion layer of 5-20 μm, in which the Al content continuously decreases from the inside to the outside, while the Si and Mg content continuously increases. This crucible, through matching the thermal expansion coefficient and buffering thermal stress at the gradient interface, achieves a cycle life of more than 30 cycles against alkali corrosion, and has excellent alkali resistance and thermal shock resistance, making it suitable for high-temperature sintering of ternary cathode materials.

Description

Technical Field

[0001] This invention relates to the field of new energy battery technology, and in particular to an aluminum titanate composite crucible, its preparation method, and its application. Background Technology

[0002] Lithium-ion battery cathode materials (such as NCM, NCA, LCO, etc.) need to be sintered at high temperatures of 900–1100℃. Simultaneously, the lithium source used (lithium carbonate or lithium hydroxide) decomposes into strongly alkaline Li₂O at high temperatures, causing severe chemical corrosion to the kiln furniture materials. Currently commonly used mullite and cordierite saggers, whose Al₂O₃ and SiO₂ components readily react with Li₂O to form lithium aluminate (LiAlO₂) and spodumene (LiAlSiO₄), lead to sagger spalling, cracking, and generally low service life (typically only 10-15 cycles), failing to meet the cost reduction and efficiency improvement requirements of the power battery industry.

[0003] Aluminum titanate (Al₂TiO₅) has a high melting point (1860℃) and an extremely low coefficient of thermal expansion (α<1.5×10⁻⁶). -6 With its excellent resistance to alkali corrosion (including negative values ​​of K), pure aluminum titanate is theoretically an ideal sagger material. However, pure aluminum titanate has two inherent drawbacks: firstly, its mechanical strength is relatively low; secondly, it easily decomposes into corundum and rutile within the temperature range of 800–1280℃, limiting its application alone. While there are reports of combining aluminum titanate with spinel, mullite, etc. (e.g., CN108033787B, CN108017387B), these are mostly single-layer homogeneous structures, making it difficult to simultaneously achieve strong alkali corrosion resistance on the inner surface and high thermomechanical strength and thermal shock resistance of the outer matrix.

[0004] Therefore, developing a composite structure crucible that can withstand strong alkali corrosion, has good thermal shock resistance, and a long service life is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] This invention proposes an aluminum titanate composite sagger, its preparation method, and its application, aiming to solve the technical problem that existing saggers cannot simultaneously meet the requirements of alkali corrosion resistance and thermal shock resistance.

[0006] In a first aspect, the present invention provides an aluminum titanate composite crucible, comprising an inner surface working layer and an outer substrate layer from the inside out; The thickness of the inner surface working layer is 1–3 mm; The inner surface working layer comprises the following raw materials in parts by weight: 20-80 parts of synthetic aluminum titanate, 5-10 parts of kaolin, 10-80 parts of spinel, 0-20 parts of alumina, 0-5 parts of organic binder, and 1-5 parts of water. The outer matrix layer comprises the following raw materials in parts by weight: 5-40 parts of M45 sintered mullite, 5-40 parts of M70 sintered mullite, and 10-20 parts of kaolin. - 5-20 parts alumina, 10-50 parts cordierite, 1-10 parts talc, 10-30 parts fused silica, 1-5 parts organic binder, and 1-5 parts water; The average coefficient of thermal expansion of the inner surface working layer material from room temperature to 1000°C is [value missing]. ≤2.0×10 -6 / K, the average coefficient of thermal expansion of the outer substrate material from room temperature to 1000℃ is And it satisfies 3.0×10 -6 / K≤ ≤5.0×10 -6 / K; The inner surface working layer and the outer substrate layer are integrally pressed and sintered to form a tightly bonded interface diffusion layer. The thickness of the interface diffusion layer is 5-20 μm. Within the interface diffusion layer, the Al element content shows a continuously decreasing gradient distribution from the inner surface working layer to the outer substrate layer, while the Si and Mg element contents show a continuously increasing gradient distribution.

[0007] The technical advantages of the aluminum titanate composite crucible disclosed in this invention are: through optimization of the outer layer formula, especially the introduction of an appropriate amount of fused silica (with an extremely low coefficient of thermal expansion, approximately 0.5 × 10⁻⁶). -6 / K) and talc (forming a low-expansion phase with cordierite), will Precisely controlled within 3.0~5.0×10 -6 Within the range of / K. This matching range is a critical threshold determined by this invention through numerous experiments: Δ <1×10 -6 At / K, the outer layer's thermal shock resistance is insufficient (due to excessive fused silica leading to a decrease in strength); Δ >3×10 -6 At / K, excessive interfacial thermal stress leads to delamination. On the other hand, through integral pressing followed by high-temperature sintering, interdiffusion occurs at the interface, spontaneously forming a continuous gradient diffusion layer with a thickness of 5–20 μm. The proportions of Al, Si, and Mg in the diffusion layer continuously change, and its coefficient of thermal expansion also varies from the inner layer. Gradient to the outer layer This eliminates abrupt interface changes, thereby significantly reducing the peak thermal stress at the interface.

[0008] Furthermore, the synthesized aluminum titanate is obtained by high-temperature synthesis from raw materials comprising the following parts by weight: 35-45 parts titanium dioxide, active... - 50-60 parts of alumina, 0-10 parts of magnesium carbonate, 0-10 parts of zirconium oxide, and 0-5 parts of spodumene; wherein the spodumene is used to suppress the thermal decomposition of aluminum titanate in the temperature range of 800-1280℃, and the zirconium oxide is used to refine the grains.

[0009] Furthermore, the spinel is magnesium aluminum spinel with a particle size of 325 mesh; the particle size distribution of the synthetic aluminum titanate is: 30-50 wt% of 200 mesh powder and 50-70 wt% of 0.5-1 mm particles.

[0010] Furthermore, the organic binder is selected from at least one of sodium lignosulfonate, xanthodextrin, carboxymethyl cellulose, and hydroxypropyl methyl cellulose.

[0011] Furthermore, the thickness ratio of the inner surface working layer to the outer substrate layer is 1:(5-15).

[0012] Furthermore, the outer substrate layer comprises the following raw materials in parts by weight: 0-13 parts of M70 sintered mullite, 10-21 parts of roller stock, and 13-16 parts of kaolin. - Alumina 8-17 parts, cordierite 20-33 parts, talc 1-2 parts, organic binder 1-5 parts, feldspar 2-5 parts, fused silica 7-27 parts, water 1-5 parts.

[0013] Secondly, the present invention provides a method for preparing the aluminum titanate composite crucible as described above, comprising the following steps: (1) Synthesis of aluminum titanate: Weigh out titanium dioxide, active aluminum titanate, and other materials according to the specified ratio. Alumina, magnesium carbonate, zirconium oxide, and spodumene are added to a ball mill at a ratio of 1:1 to 1.2. After being mixed evenly, the mixture is sintered at 1300 to 1400°C for 1 to 5 hours to obtain aluminum titanate clinker. After crushing, sieving, and ball milling, 200-mesh powder and 0.5 to 1 mm particles are obtained. (2) Preparation of inner surface working layer material: Weigh synthetic aluminum titanate, kaolin, spinel and alumina according to the ratio, and premix them evenly; dissolve the organic binder in water to obtain a binder solution; mix the premixed material and the binder solution evenly, age for 12-24 hours, and pass through a 2-3 mesh sieve to obtain the inner surface working layer material; (3) Preparation of outer matrix layer material: Weigh M45 sintered mullite, M70 sintered mullite, kaolin, according to the proportion. - Alumina, cordierite, talc, and fused silica are premixed evenly; an organic binder is dissolved in water to obtain a binder solution; the premix and binder solution are mixed evenly, aged for 12-24 hours, and passed through a 2-3 mesh sieve to obtain the outer matrix layer material; (4) Integrated pressing: The outer substrate material is first added into the mold and leveled, then the inner surface working layer material is added and leveled. Under pressure of 80-200MPa, double-sided pressure is applied and held for 10-30s to press and form the sagger green. (5) Sintering: Dry the green billet at 110-120℃ for 12-24h, then heat it to 1300-1400℃ at a heating rate of 1-3℃ / min, hold it for 2-8h, and cool it with the furnace to obtain aluminum titanate composite sagger.

[0014] The technical effect of the preparation method disclosed in this invention is that the continuous gradient interface diffusion layer is spontaneously formed by the inner and outer layer elements during the sintering process, which effectively buffers the interface thermal stress caused by the difference in thermal expansion coefficient, thereby increasing the alkali erosion resistance cycle life of the composite sagger to more than 30 times, and achieving synergistic effect of alkali resistance and thermal shock resistance.

[0015] Thirdly, the present invention also provides an application of the aluminum titanate composite crucible as described above in the preparation of cathode materials, wherein the cathode material is a nickel-cobalt-manganese ternary cathode material or a lithium cobalt oxide cathode material. Attached Figure Description

[0016] Figure 1 This is a process flow diagram of the preparation method of the present invention; Figure 2 The results of the 5-series precursor + Li2CO3 test in the alkaline corrosion resistance test of Comparative Example 1 are shown in the figure. Figure 3 The results of the 5-series precursor + Li2CO3 test in Example 3 are shown in the figure. Figure 4 The result of the 5-series precursor + Li2CO3 test in Example 2 is shown in the figure. Figure 5 The results of the 5-series precursor + Li2CO3 test in Example 1 are shown in the figure. Figure 6 The results of the 8 / 9 series precursor + LiOH·H2O test in the alkaline corrosion resistance test of Comparative Example 1 are shown in the figure. Figure 7 The image shows the results of the 8 / 9 series precursor + LiOH·H2O test in Example 3 for resistance to alkaline corrosion. Figure 8 The image shows the results of the 8 / 9 series precursor + LiOH·H2O test in Example 2 for resistance to alkaline corrosion. Figure 9 The image shows the results of the 8 / 9 series precursor + LiOH·H2O test in Example 1. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] To address the problem mentioned in the background art that aluminum titanate composite saggers cannot simultaneously achieve strong resistance to alkali corrosion on the inner surface and high thermomechanical strength and thermal shock resistance of the outer substrate, this invention provides an aluminum titanate composite sagger. In the following embodiments and comparative examples, unless otherwise specified, all raw materials used are commercially available refractory materials with a purity ≥95%. Specific specifications are as follows: Titanium dioxide: Rutile nano titanium dioxide, TiO2 purity > 99.5%, average particle size 200nm.

[0019] active - Alumina: purity ≥ 99%, average particle size ≤ 5 μm.

[0020] Magnesium aluminum spinel: 325 mesh (44μm), MgO content 28-32%.

[0021] M45 sintered mullite: Al2O3 content 45-48%, bulk density ≥2.6g / cm³.

[0022] M70 sintered mullite: Al2O3 content 70-73%, bulk density ≥2.8g / cm³.

[0023] Cordierite: 2MgO·2Al2O3·5SiO2, with a thermal expansion coefficient of approximately 1.5-2.5×10⁻⁶. -6 / K.

[0024] Fused silica: SiO2 content ≥ 99%, coefficient of thermal expansion approximately 0.5 × 10⁻⁶ -6 / K.

[0025] Kaolin: Al2O3 content ≥38%, bound clay.

[0026] Talc: MgO content ≥30%.

[0027] Organic binder: Carboxymethyl cellulose (CMC) or xanthodextrin, industrial grade.

[0028] Test standards and methods: (1) Alkali corrosion resistance cycle life test: A high-nickel 811 ternary precursor (Ni) was loaded into the inner cavity of the crucible. 0˙8 Co 0˙1 Mn 0˙1A mixture of (OH)₂ and LiOH·H₂O (mass ratio 1:0.5) was placed in a resistance furnace and heated to 980℃ at a rate of 5℃ / min, held for 10 hours, and then cooled to room temperature with the furnace. The material was then removed, constituting one cycle. After each cycle, the inner surface of the crucible was observed: if spalling pits with a diameter >5mm, through-cracks, or severe adhesion between the material and the crucible made it impossible to separate occurred, it was considered a failure. The number of cycles at the point of failure was recorded. Three parallel samples were tested in each group, and the average value was taken. For the 5-series precursor + Li₂CO₃ system, the test conditions were similar, with a sintering temperature of 1000℃.

[0029] (2) Thermal shock resistance test: The crucible is heated to 1100℃ and kept at that temperature for 30 minutes. Then it is quickly removed and immersed in flowing cold water at 25±2℃, which constitutes one thermal shock cycle. After every 5 cycles, the surface of the crucible is checked, and the number of times a visible crack appears is recorded. Each sample is tested 3 times, and the average value is taken.

[0030] (3) Interfacial shear strength test: A 10mm × 10mm cubic specimen was cut from the bottom of the composite crucible, with the interface located in the middle of the specimen. Using a universal testing machine, a shear force was applied to the interface at a loading rate of 0.5mm / min. The maximum failure load was recorded and divided by the interface area (10mm × 10mm) to obtain the shear strength. Five specimens were tested for each example / comparative example, and the average value was taken.

[0031] (4) Thermal expansion coefficient test: Separate samples of inner and outer layer materials were prepared (pressing and sintering regimes were the same as the corresponding saggers), and processed into cylinders of Φ6mm×25mm. The average linear expansion coefficient from room temperature to 1000℃ was recorded using a thermal expansion meter (NETZSCHDIL402C) at a rate of 5℃ / min in air atmosphere. (10) -6 / K).

[0032] (5) Interface microstructure analysis: Take the cross section of the sagger, grind, polish, and heat etch (hold at 1300℃ for 10 min), observe the interface morphology using a scanning electron microscope (SEM, ZEISS Gemini300), and perform line scanning elemental analysis with an energy dispersive spectrometer (EDS, Oxford X-Max).

[0033] (6) Decomposition rate test of aluminum titanate: The synthesized aluminum titanate powder (200 mesh) was kept at 1200℃ for 10h. The diffraction peak intensities of corundum (Al2O3) and rutile (TiO2) were quantitatively analyzed by X-ray diffraction (XRD) to calculate the decomposition rate. Decomposition rate = (I(corundum) + I(rutile)) / (I(aluminum titanate) + I(corundum) + I(rutile)) × 100%.

[0034] Example 1: Inner layer TiAl / spinel = 40 / 50 (40 parts aluminum titanate, 50 parts spinel) (a) Synthesis of aluminum titanate: Weigh 40 parts by weight of titanium dioxide and active... Alumina (55 parts by weight), magnesium carbonate (3 parts by weight), and zirconium oxide (2 parts by weight, 0 parts by weight) were added to a planetary ball mill at a material-to-ball ratio of 1:1.1 and a speed of 30 rpm for 2 hours. The mixture was then placed in an alumina crucible and held at 1350℃ for 3 hours in a gas-fired kiln. The resulting aluminum titanate clinker was subjected to jaw crushing, roller crushing, and sieving to obtain 0.5–1 mm particles; the undersize material was further ball-milled to a 200-mesh (75 μm) powder. The average coefficient of thermal expansion of this aluminum titanate from room temperature to 1000℃ was measured to be 1.9 × 10⁻⁶. -6 / K.

[0035] (II) Preparation of the inner surface working layer material: Weigh 20 parts by weight of synthetic aluminum titanate 200 mesh powder, 20 parts by weight of synthetic aluminum titanate 0.5-1 mm particles, 50 parts by weight of magnesium aluminum spinel (325 mesh), and 8 parts by weight of kaolin. - 2 parts by weight of alumina. Add the powder to a high-performance mixer and dry mix for 3 minutes. Separately, take 1 part by weight of carboxymethyl cellulose (CMC), dissolve it in 3 parts by weight of water, and stir for 30 minutes to obtain a binder solution. Add the binder solution to the powder and continue mixing for 8 minutes. After discharging, seal and age for 18 hours, then pass through a 3-mesh sieve (6.7 mm) to obtain the inner surface working layer material.

[0036] (III) Preparation of the outer matrix layer material: Weigh 15 parts by weight of M45 sintered mullite, 15 parts by weight of M70 sintered mullite, and 35 parts by weight of cordierite. - 10 parts by weight of alumina, 15 parts by weight of kaolin, 1 part by weight of talc, and 9 parts by weight of fused silica. Premix the powder for 3 minutes. Separately, dissolve 2 parts by weight of dextrin in 3 parts by weight of water and stir for 30 minutes. Add the binder solution to the powder, mix for 8 minutes, age for 18 hours, and pass through a 3-mesh sieve to obtain the outer matrix layer material. Independent sample testing showed that the average coefficient of thermal expansion of this outer layer material from room temperature to 1000℃ is 4.2 × 10⁻⁶. -6 / K.

[0037] (iv) Integrated pressing: The outer substrate material is evenly filled into the bottom of the steel mold (internal cavity size 200mm×200mm×15mm), leveled, and the material layer thickness is about 13mm. Then, the inner working layer material is evenly spread on top, leveled, and designed to be 2mm thick. The mold is then pressed on both sides at 120MPa on a hydraulic press, held for 20s, and demolded to obtain the green blank.

[0038] (V) Drying and Sintering: The green blanks were dried in a forced-air drying oven at 120℃ for 24 hours. Then they were placed in a shuttle kiln and sintered according to the following regime: room temperature → 600℃, heating rate 2℃ / min, holding for 1 hour (to allow the organic binder to be completely carbonized and discharged); 600℃ → 1360℃, heating rate 2.5℃ / min, holding for 4 hours; and then naturally cooled to room temperature with the furnace. The aluminum titanate composite sagger was obtained.

[0039] Example 2: Inner layer TiAl / spinel = 65 / 25 (65 parts aluminum titanate, 25 parts spinel) The formulation is basically the same as in Example 1, except for the inner surface working layer: 32.5 parts by weight of synthetic aluminum titanate 200 mesh powder, 32.5 parts by weight of synthetic aluminum titanate 0.5-1mm particles, 25 parts by weight of magnesium aluminum spinel, and 8 parts by weight of kaolin. - 2 parts by weight of alumina (65 parts total of aluminum titanate and 25 parts spinel in the inner layer). The inner layer thickness remains 2 mm. The outer layer formulation is the same as in Example 1. Test results are shown in Table 1.

[0040] Example 3: Inner layer TiAl / spinel = 80 / 10 (80 parts aluminum titanate, 10 parts spinel) The formulation is basically the same as in Example 1, except for the inner surface working layer: 40 parts by weight of synthetic aluminum titanate 200 mesh powder, 40 parts by weight of synthetic aluminum titanate 0.5-1mm particles, 10 parts by weight of magnesium aluminum spinel, and 8 parts by weight of kaolin. - 2 parts by weight of alumina (80 parts total of aluminum titanate and 10 parts spinel in the inner layer). The inner layer is designed to be 2 mm thick. The outer layer formulation is the same as in Example 1. Test results are shown in Table 1.

[0041] Example 4: Inner layer TiAl / spinel = 20 / 70 (20 parts aluminum titanate, 70 parts spinel) — used to verify the lower limit of aluminum titanate. The formula is basically the same as in Example 1, except for the inner surface working layer: 10 parts of 200-mesh synthetic aluminum titanate powder, 10 parts of 0.5-1mm synthetic aluminum titanate particles, 70 parts of magnesium aluminum spinel, and 8 parts of kaolin. - 2 parts alumina. Inner layer thickness 2mm. Outer layer formulation same as in Example 1.

[0042] Example 5: Synthesis of aluminum titanate containing spodumene (inner TiAl / spinel = 80 / 10) The process is essentially the same as in Example 3, except that spodumene is added to the raw materials for synthesizing aluminum titanate. Specifically, it consists of 40 parts by weight of titanium dioxide, active... - 53 parts by weight of alumina, 2 parts by weight of magnesium carbonate, 2 parts by weight of zirconium oxide, and 3 parts by weight of spodumene. The sintering process was the same as in Example 1. The average coefficient of thermal expansion of this aluminum titanate from room temperature to 1000°C was tested to be 1.2 × 10⁻⁶.-6 / K; The decomposition rate after holding at 1200℃ for 10 hours was 5%. The remaining steps (inner layer formulation, outer layer formulation, molding, sintering) were exactly the same as in Example 3. The test results are shown in Table 1.

[0043] Comparative Example 1: Single-layer inner layer material Only the inner surface working layer material (TiAl / spinel = 80 / 10) from Example 3 was used, without an outer layer. The material was directly filled into the mold with a designed thickness of 15 mm, pressed at 120 MPa, and after drying, sintered using the same sintering process as in Example 1. A single-layer sagger was obtained. The test results are shown in Table 1.

[0044] Comparative Example 2: Single-layer outer material Only the outer substrate material from Example 1 was used, without an inner layer. The material was directly filled into the mold, with a designed thickness of 15 mm, and pressed into shape at 120 MPa. After the green body was dried, it was sintered using the exact same sintering process as in Example 1. A single-layer sagger was obtained. The test results are shown in Table 1.

[0045] Comparative Example 3: Inner layer thickness is too thick (5mm) The results were basically the same as in Example 3 (inner layer formulation TiAl / spinel = 80 / 10), except that the thickness of the inner surface working layer was 5 mm, and the thickness of the outer substrate layer was reduced to 10 mm, while the total thickness remained unchanged at 15 mm. The test results are shown in Table 1.

[0046] Comparative Example 4: Inner layer thickness is too thin (0.5mm) The experiment was basically the same as in Example 3, except that the thickness of the inner working layer was 0.5 mm and the thickness of the outer substrate layer was 14.5 mm. The test results are shown in Table 1.

[0047] Comparative Example 5: The outer layer has an excessively high coefficient of thermal expansion (no gradient design). The formula is basically the same as Example 3 (inner layer formulation: TiAl / spinel = 80 / 10, inner layer thickness: 2mm), except that fused silica is removed from the outer matrix layer formulation, and the amount of cordierite is increased in an attempt to improve thermal shock resistance. Specifically, it consists of 15 parts M45 mullite, 15 parts M70 mullite, and 60 parts cordierite. - 10 parts alumina, 15 parts kaolin, and 1 part talc (without fused silica). Independent sample testing showed that the average coefficient of thermal expansion of this outer layer material is 6.5 × 10⁻¹⁰ °C from room temperature to 1000 °C. -6 / K, the difference between the inner layer and the inner layer is Δα = 4.7 × 10 -6 / K. The other steps are the same. The test results are shown in Table 1.

[0048] Comparative Example 6: Non-monolithic molding (molded separately and then bonded together) The same inner and outer layer formulations as in Example 3 were used. Inner layer sheets (2 mm thick) and outer layer sheets (13 mm thick) were pressed separately at a pressure of 120 MPa. The pressed inner and outer layer sheets were bonded together using a commercially available high-temperature adhesive (water glass, Na2SiO3), cured at 120°C for 2 hours, and then sintered according to the same sintering regime as in Example 1. The test results are shown in Table 1.

[0049] Comparative Example 7 (Additional Supplement): Inner layer thickness 2mm, but outer layer thermal expansion coefficient too low (3.0×10⁻⁶). -6 (below / K) The formulation is essentially the same as Example 3, except that the outer matrix layer composition includes 30 parts fused quartz and 15 parts cordierite. Testing revealed that the outer layer... =2.8×10 -6 / K, the difference between the inner layer and Δ =1.0×10 -6 / K. Test results show that the crucible has a 25-cycle lifespan against alkali corrosion, but only 18 cycles against thermal shock, and microcracks appear on the outer surface. This indicates that when the outer layer's thermal expansion coefficient is too low, its thermal shock resistance decreases (low-expansion materials usually have lower strength) and it cannot withstand the thermal shock of rapid cooling.

[0050] Comparative Example 1: Single-layer inner layer material Only the inner surface working layer material (TiAl / spinel = 80 / 10) from Example 3 was used, without an outer layer. The material was directly filled into the mold with a designed thickness of 15 mm, pressed at 120 MPa, and after drying, sintered using the same sintering process as in Example 1. A single-layer sagger was obtained.

[0051] Comparative Example 2: Single-layer outer material Only the outer substrate material from Example 1 was used, without an inner layer. The material was directly filled into a mold with a designed thickness of 15 mm, pressed at 120 MPa, and after drying, sintered using the same sintering process as in Example 1. A single-layer sagger was obtained.

[0052] Comparative Example 3: Inner layer thickness is too thick (5mm) It is basically the same as Example 3 (inner layer formula TiAl / spinel=80 / 10), except that the thickness of the inner surface working layer is 5mm, the thickness of the outer substrate layer is reduced to 10mm, and the total thickness remains unchanged at 15mm.

[0053] Comparative Example 4: Inner layer thickness is too thin (0.5mm) It is basically the same as Example 3, except that the thickness of the inner working layer is 0.5 mm and the thickness of the outer substrate layer is 14.5 mm.

[0054] Comparative Example 5: The outer layer has an excessively high coefficient of thermal expansion (no gradient design). The formula is basically the same as Example 3 (inner layer formula TiAl / spinel = 80 / 10, inner layer thickness 2mm), the difference being that fused silica is removed from the outer matrix layer formula and the amount of cordierite is increased, specifically: 15 parts M45 mullite, 15 parts M70 mullite, and 60 parts cordierite. - 10 parts alumina, 15 parts kaolin, and 1 part talc (without fused silica). Independent sample testing showed that the average coefficient of thermal expansion of this outer layer material is 6.5 × 10⁻¹⁰ °C from room temperature to 1000 °C. -6 / K, the difference Δ between the inner layer and the inner layer =4.7×10 -6 / K.

[0055] Comparative Example 6: Non-monolithic molding (molded separately and then bonded together) The same inner and outer layer formulations as in Example 3 were used. Inner layer sheets (2 mm thick) and outer layer sheets (13 mm thick) were pressed separately at a pressure of 120 MPa. The pressed inner and outer layer sheets were bonded together using a commercially available high-temperature adhesive (water glass, Na2SiO3), cured at 120°C for 2 hours, and then sintered according to the same sintering regime as in Example 1.

[0056] Comparative Example 7: The outer layer's coefficient of thermal expansion is too low ( =2.8×10 -6 / K) The formulation is essentially the same as Example 3, except that the outer matrix layer composition includes 30 parts fused quartz and 15 parts cordierite. Testing revealed that the outer layer... =2.8×10 -6 / K, the difference between the inner layer and Δ =1.0×10 -6 / K.

[0057] Comparative Example 8: The content of aluminum titanate in the inner layer is below the lower limit (15 parts aluminum titanate, 75 parts spinel). The composition is basically the same as in Example 1, except for the formulation of the inner surface working layer: 7.5 parts of synthetic aluminum titanate 200 mesh powder, 7.5 parts of synthetic aluminum titanate 0.5-1mm particles, 75 parts of magnesium aluminum spinel, and 8 parts of kaolin. - Alumina 2 parts. Total aluminum titanate 15 parts, spinel 75 parts.

[0058] Comparative Example 9: The content of aluminum titanate in the inner layer is higher than the upper limit (85 parts aluminum titanate, 5 parts spinel). An attempt was made to prepare an inner layer material with a TiAl / spinel ratio of 85 / 5, but it was difficult to mix uniformly in a high-intensity mixer. Delamination occurred during green forming, and the sintered sample showed obvious cracking, making subsequent testing impossible. This indicates that when the aluminum titanate content exceeds 80 parts, the forming and sintering properties of the inner layer material deteriorate significantly.

[0059] Comparative Example 10: Kaolin content below the lower limit (3 samples) The results were essentially the same as in Example 3, except that the amount of kaolin in the inner working layer was 3 parts. Test results showed that the room temperature flexural strength of the inner working layer of the crucible decreased from 15.2 MPa to 9.8 MPa, and the alkali erosion cycle life decreased from 30 cycles to 18 cycles. The failure mode was inner layer spalling, indicating insufficient bonding strength.

[0060] Comparative Example 11: Kaolin content exceeds the upper limit (12 samples) The results were essentially the same as in Example 3, except that the amount of kaolin in the inner working layer was 12 parts. Test results showed that the apparent porosity of the inner layer increased from 18% to 26%, the alkali corrosion resistance cycle life decreased to 16 cycles, and the failure mode was alkali penetration corrosion. XRD analysis showed that the glass phase content in the inner layer increased, and the alkali corrosion resistance decreased.

[0061] Comparative Example 12: Alumina content exceeds the upper limit (25 samples) It is basically the same as Example 3, except that in the inner surface working layer The amount of alumina used was 25 parts (correspondingly reducing the amount of synthesized aluminum titanate). Test results showed that the inner layer's coefficient of thermal expansion... From 1.8×10 -6 / K increased to 2.4×10 -6 / K, and outer Δ Reduced to 1.8 × 10 -6 / K, the interfacial shear strength is slightly improved (5.1MPa), but the cost increases by about 15%, while the alkali erosion resistance life only increases slightly from 30 cycles to 31 cycles, which is not significant and not economical.

[0062] Table 1 Performance test results of the examples and comparative examples Among them, (1) is about the determination of the ratio range of aluminum titanate / spinel in the inner layer. A comparison of Examples 1, 2, 3, 4 and Comparative Example 8 shows that: When the aluminum titanate content is 20 parts (70 parts spinel, Example 4), =2.3×10 -6 / K, although the interface matches well (Δ =1.9), but the spinel content in the inner layer is too high, which leads to a decrease in the intrinsic alkali resistance of the inner layer (although spinel is more alkali resistant than mullite, it is not as alkali resistant as aluminum titanate), and the lifespan is 28 times, which is lower than Example 1 (35 times).

[0063] When the aluminum titanate content is 40 parts (Example 1) and 65 parts (Example 2), the lifespan reaches 35 cycles and 32 cycles respectively, which is the optimal range. In 1.8-1.9×10 -6 Between / K, and =4.2×10 -6 / K of Δ =2.3-2.4, which ensures sufficient alkali resistance, maintains good interface matching, and the inner layer itself has good sintering density (porosity 17-19%).

[0064] When the aluminum titanate content was 80 parts (Example 3), the lifespan decreased to 30 cycles, but was still within an acceptable range. At this point, the excessive aluminum titanate content resulted in a slight decrease in the inner layer strength (the room temperature flexural strength decreased from 15.2 MPa in Example 1 to 12.5 MPa), and the particle size distribution requirements were more stringent during green body forming.

[0065] When the aluminum titanate content was reduced to 15 parts (Comparative Example 8), the lifespan was only 22 cycles, and microcracks appeared in the inner layer because... Increased to 2.5 × 10 -6 / K, the inner layer's own thermal expansion coefficient increases, generating internal stress during the sintering and cooling process.

[0066] When the aluminum titanate content increased to 85 parts (Comparative Example 9), the material could not be formed normally, indicating that the upper limit of the process was 80 parts.

[0067] Therefore, the present invention limits the range of aluminum titanate to 20-80 parts, preferably 40-65 parts, which is based on sufficient experimental evidence.

[0068] (2) Determination of the range of kaolin content. Comparative Example 10 (3 parts kaolin) showed insufficient inner layer bonding strength, resulting in a lifespan of 18 cycles; Comparative Example 11 (12 parts kaolin) showed an increase in glass phase, higher porosity, and decreased resistance to alkali erosion, with a lifespan of 16 cycles. In Examples 1-3, 8 parts kaolin yielded the best results. Therefore, 5-10 parts is a feasible range, with 7-9 parts being optimal.

[0069] (3) - Determining the range of alumina content. Comparative Example 12 (25 parts alumina) showed limited performance improvement but a significant increase in cost. The addition of alumina can improve the purity of the inner layer and adjust the coefficient of thermal expansion, but the marginal benefit diminishes after exceeding 20 parts. A range of 0 to 20 parts is reasonable, with 2 to 10 parts being preferred.

[0070] (4) Comparison of critical inner layer thickness between Comparative Example 3 (5 mm) and Example 3 (2 mm): At 5 mm, the interface diffusion layer is thick (15 μm) but discontinuous, the shear strength drops to 2.1 MPa, and the lifespan is only 15 cycles; while in Comparative Example 4 (0.5 mm), the interface is discontinuous, the alkali solution penetrates rapidly, and the lifespan is 12 cycles.

[0071] (5) Coefficient of thermal expansion of outer layer Determining the scope. Comparative Example 5 ( =6.5)Δ The shear strength was too high, with an interfacial shear strength of only 1.5 MPa and a lifespan of 18 cycles, but it failed due to interfacial peeling; Comparative Example 7 ( Although the interface is good (=2.8), the outer layer's thermal shock resistance is reduced (18 cycles), and its strength is also lower. Shear strength is... The thermal shock resistance remains high (>4.5 MPa) between 3.0 and 5.0, while the outer layer's thermal shock resistance also peaks within this range (>30 cycles). Therefore... =3.0~5.0×10 -6 / K represents the optimal range considering both interface matching and thermal shock resistance, with the optimal value being 4.0–4.5 × 10⁻⁶. -6 / K.

[0072] (6) Effect of adding spodumene. Compared with Example 3, after adding 3 parts of spodumene in Example 5: the decomposition rate of aluminum titanate decreased from 18% to 5%, and the coefficient of thermal expansion decreased from 1.8 to 1.2×10. -6 / K, lifespan increased from 30 cycles to 38 cycles, and thermal shock resistance increased from 28 cycles to 32 cycles. The addition of spodumene further optimized the performance; an addition amount of 0-5 parts is reasonable, with 2-4 parts being preferred.

[0073] This continuous compositional gradient implies a gradient transition in the coefficient of thermal expansion within the diffusion layer. By individually testing the thermal expansion of micro-regions at different locations (nanoindentation combined with thermomechanical analysis), it was confirmed that the coefficient of thermal expansion of the diffusion layer ranges from 1.9 × 10⁻⁶ in the inner layer. -6 / K continuously varies up to 4.2×10 in the outer layer. -6 / K. This gradient eliminates the thermal stress concentration caused by abrupt performance changes in traditional double-layer structures, resulting in an interfacial shear strength of 5.2 MPa.

[0074] Comparative Example 6 showed an interfacial shear strength of only 0.8 MPa, demonstrating the crucial role of the integral pressing molding process in this invention. In Comparative Example 5, due to Δ... If the size is too large, the resulting diffusion layer will be discontinuous (only 3μm and with microcracks) and will not be able to effectively buffer thermal stress.

[0075] The following tests were conducted on the alkaline corrosion resistance of Examples 1 to 3 and Comparative Example 1, with the results of the 5-series precursor + Li2CO3 (ternary 5-series (NCM523) precursor + lithium carbonate) as shown in Table 2: The results of 8 / 9 series precursor + LiOH·H2O (ternary 8 series (NCM811) or 9 series precursor + lithium hydroxide) are shown in Table 3 below: The core technical features of this invention are as follows: Feature 1: Precise matching of the thermal expansion coefficients of the inner and outer layers.

[0076] This invention requires the inner surface working layer material to have an average coefficient of thermal expansion from room temperature to 1000°C. ≤2.0×10 -6 / K, the average coefficient of thermal expansion of the outer substrate material from room temperature to 1000℃. Satisfies 3.0×10 -6 / K≤ ≤5.0×10 -6 / K.

[0077] As is known to those skilled in the art, aluminum titanate-based materials It can be as low as 1.0×10 -6 / K can even be negative, while mullite-cordierite based materials Typically between 4.0 and 6.5 × 10⁻⁶ -6 / K. If the two layers are simply combined, the difference in the coefficient of thermal expansion (ΔK) = - It could be as high as 4×10 -6 Above / K. During repeated high-temperature sintering-cooling cycles (room temperature → 1000℃ → room temperature), periodic alternating thermal stresses will be generated at the interface. According to the thermal stress formula σ=E·Δ ·ΔT, when Δ When the stress is too high, the interfacial shear stress σ will exceed the bonding strength of the material, leading to delamination or cracking.

[0078] This invention optimizes the outer layer formulation, particularly by introducing an appropriate amount of fused silica (with an extremely low coefficient of thermal expansion, approximately 0.5 × 10⁻⁶). -6 / K) and talc (forming a low-expansion phase with cordierite), will Precisely controlled within 3.0~5.0×10 -6 Within the range of / K, such that Δ Controlled between 1 and 3 × 10 -6 / K. This matching range is a critical threshold determined by this invention through numerous experiments: Δ <1×10 -6 At / K, the outer layer's thermal shock resistance is insufficient (due to excessive fused silica leading to a decrease in strength); Δ >3×10 -6 At / K, excessive interfacial thermal stress leads to delamination (see Comparative Example 5).

[0079] Feature 2: Gradient interface diffusion layer formed by integral pressing.

[0080] This invention employs an integrated pressing process, sequentially adding the inner and outer layers into the same mold for one-time pressing and then high-temperature sintering. During this process, due to the difference in chemical potential between Al, Si, and Mg elements in the inner and outer layers, mutual diffusion occurs at the interface, spontaneously forming a continuous gradient diffusion layer with a thickness of 5–20 μm. From the inner working layer to the outer substrate layer, the Al content gradually decreases (from approximately 70% to approximately 40%), while the Si and Mg content gradually increases (Si from approximately 10% to approximately 25%, and Mg from approximately 2% to approximately 10%). This gradient diffusion layer acts as a "thermal expansion coefficient buffer layer": the continuous change in the proportion of Al, Si, and Mg in the diffusion layer also affects its thermal expansion coefficient from the inner layer... Gradient to the outer layer This eliminates abrupt interface changes, thereby significantly reducing the peak thermal stress at the interface.

[0081] Feature 3: The critical value of inner layer thickness is 1-3 mm.

[0082] The thickness of the inner layer is another key parameter affecting the performance of the double-layer structure. This invention experimentally determined that when the inner layer thickness is <1mm (Comparative Example 4), although the thermal stress is low, the inner layer is too thin, allowing alkaline solution to easily penetrate to the outer layer through micropores, leading to corrosion and failure of the outer layer. When the inner layer thickness is >3mm (Comparative Example 3), due to the extremely low intrinsic thermal expansion coefficient of the aluminum titanate-based material, the excessively thick inner layer accumulates significant shrinkage stress during cooling. This stress cannot be completely buffered by the outer layer, leading to the initiation of radial cracks. Only when the inner layer thickness is controlled between 1 and 3mm does the balance between alkali corrosion resistance and thermal stress reach its optimal level.

[0083] Feature 4: Functional additives in the synthesis of aluminum titanate.

[0084] This invention introduces spodumene (0-5 parts) and zirconium oxide (0-10 parts) into the synthesis of aluminum titanate. Spodumene (LiAlSi2O6) has an extremely low coefficient of thermal expansion (approximately 0.5 × 10⁻⁶). -6Zirconia ( / K) can enter the aluminum titanate lattice to form a solid solution, inhibiting the decomposition reaction of aluminum titanate in the temperature range of 800–1280℃ (the decomposition products corundum and rutile will impair the alkali resistance). Example 4 confirms that after adding 3 parts of spodumene, the decomposition rate of aluminum titanate at 1200℃ for 10 hours decreased from 18% to 5%. Zirconia, as a grain refiner, pins grain boundaries, inhibits abnormal grain growth in aluminum titanate, and improves thermal shock resistance.

[0085] This invention determined the key parameter range and optimal values ​​of the double-layer composite sagger through systematic experiments: Inner layer aluminum titanate / spinel ratio: 20-80 / 10-80, preferably 40-65 / 25-50. Below 20 parts, insufficient alkali resistance leads to inner layer cracking; above 80 parts, molding is impossible.

[0086] Kaolin: 5-10 parts, preferably 7-9 parts. Less than 5 parts results in insufficient bonding strength, while more than 10 parts leads to excessive glass phase and increased porosity.

[0087] Inner layer thickness: 1–3 mm, preferably 2 mm. Less than 1 mm will result in alkali penetration, and more than 3 mm will cause thermal stress cracking.

[0088] outer thermal expansion coefficient 3.0~5.0×10 -6 / K, preferably 4.0~4.5×10 -6 / K. Below 3.0, the thermal shock resistance of the outer layer decreases; above 5.0, Δ Excessive interface stripping.

[0089] Spodumene: 0-5 parts, preferably 2-4 parts, can inhibit the decomposition of aluminum titanate and reduce... .

[0090] Example embodiments have been disclosed herein, and while specific terminology has been used, it is for illustrative purposes only and should be construed as such, and is not intended to be limiting. In some instances, it will be apparent to those skilled in the art that features, characteristics, and / or elements described in conjunction with particular embodiments may be used alone, or in combination with features, characteristics, and / or elements described in conjunction with other embodiments, unless otherwise expressly indicated. Therefore, those skilled in the art will understand that various changes in form and detail may be made without departing from the scope of the invention as set forth in the appended claims.

Claims

1. An aluminum titanate composite sagger, characterized in that, It includes an inner working layer and an outer substrate layer, from the inside out; The thickness of the inner surface working layer is 1–3 mm; The inner surface working layer comprises the following raw materials in parts by weight: 20-80 parts of synthetic aluminum titanate, 5-10 parts of kaolin, 10-80 parts of spinel, 0-20 parts of alumina, 0-5 parts of organic binder, and 1-5 parts of water. The outer matrix layer comprises the following raw materials in parts by weight: 5-40 parts of M45 sintered mullite, 5-40 parts of M70 sintered mullite, and 10-20 parts of kaolin. - 5-20 parts alumina, 10-50 parts cordierite, 1-10 parts talc, 10-30 parts fused silica, 1-5 parts organic binder, and 1-5 parts water; The average coefficient of thermal expansion of the inner surface working layer material from room temperature to 1000°C is [value missing]. ≤2.0×10 -6 / K, the average coefficient of thermal expansion of the outer substrate material from room temperature to 1000℃ is And it satisfies 3.0×10 -6 / K≤ ≤5.0×10 -6 / K; The inner surface working layer and the outer substrate layer are integrally pressed and sintered to form a tightly bonded interface diffusion layer. The thickness of the interface diffusion layer is 5-20 μm. Within the interface diffusion layer, the Al element content shows a continuously decreasing gradient distribution from the inner surface working layer to the outer substrate layer, while the Si and Mg element contents show a continuously increasing gradient distribution.

2. The method according to claim 1, characterized in that, The synthesized aluminum titanate is obtained by high-temperature synthesis from raw materials comprising the following parts by weight: 35-45 parts titanium dioxide, active... - 50-60 parts of alumina, 0-10 parts of magnesium carbonate, 0-10 parts of zirconium oxide, and 0-5 parts of spodumene; wherein the spodumene is used to suppress the thermal decomposition of aluminum titanate in the temperature range of 800-1280℃, and the zirconium oxide is used to refine the grains.

3. The method according to claim 1, characterized in that, The spinel is magnesium aluminum spinel with a particle size of 325 mesh; the particle size distribution of the synthetic aluminum titanate is: 30-50 wt% of 200 mesh powder and 50-70 wt% of 0.5-1 mm particles.

4. The method according to claim 1, characterized in that, The organic binder is selected from at least one of sodium lignosulfonate, xanthodextrin, carboxymethyl cellulose, and hydroxypropyl methyl cellulose.

5. The method according to claim 1, characterized in that, The thickness ratio of the inner surface working layer to the outer substrate layer is 1:(5-15).

6. The method according to claim 1, characterized in that, The outer matrix layer comprises the following raw materials in parts by weight: 0-13 parts of M70 sintered mullite, 10-21 parts of roller stock, and 13-16 parts of kaolin. - Alumina 8-17 parts, cordierite 20-33 parts, talc 1-2 parts, organic binder 1-5 parts, feldspar 2-5 parts, fused silica 7-27 parts, water 1-5 parts.

7. A method for preparing an aluminum titanate composite sagger as described in any one of claims 1 to 6, characterized in that, Includes the following steps: (1) Synthesis of aluminum titanate: Weigh out titanium dioxide, active aluminum titanate, and other materials according to the specified ratio. Alumina, magnesium carbonate, zirconium oxide, and spodumene are added to a ball mill at a ratio of 1:1 to 1.

2. After being mixed evenly, the mixture is sintered at 1300 to 1400°C for 1 to 5 hours to obtain aluminum titanate clinker. After crushing, sieving, and ball milling, 200-mesh powder and 0.5 to 1 mm particles are obtained. (2) Preparation of inner surface working layer material: Weigh synthetic aluminum titanate, kaolin, spinel and alumina according to the ratio, and premix them evenly; dissolve the organic binder in water to obtain a binder solution; mix the premixed material and the binder solution evenly, age for 12-24 hours, and pass through a 2-3 mesh sieve to obtain the inner surface working layer material; (3) Preparation of outer matrix layer material: Weigh M45 sintered mullite, M70 sintered mullite, kaolin, according to the proportion. - Alumina, cordierite, talc, and fused silica are premixed evenly; an organic binder is dissolved in water to obtain a binder solution; the premix and binder solution are mixed evenly, aged for 12-24 hours, and passed through a 2-3 mesh sieve to obtain the outer matrix layer material; (4) Integrated pressing: The outer substrate material is first added into the mold and leveled, then the inner surface working layer material is added and leveled. Under pressure of 80-200MPa, double-sided pressure is applied and held for 10-30s to press and form the sagger green. (5) Sintering: Dry the green billet at 110-120℃ for 12-24h, then heat it to 1300-1400℃ at a heating rate of 1-3℃ / min, hold it for 2-8h, and cool it with the furnace to obtain aluminum titanate composite sagger.

8. The preparation method according to claim 7, characterized in that, In step (5), the sintering is divided into two stages: the first stage is to raise the temperature from room temperature to 600℃ at a rate of 1-2℃ / min and hold for 1 hour; the second stage is to raise the temperature to 1300-1400℃ at a rate of 2-3℃ / min and hold for 3-5 hours.

9. The application of an aluminum titanate composite crucible as described in any one of claims 1 to 6 in the preparation of positive electrode materials, characterized in that, The cathode material is a nickel-cobalt-manganese ternary cathode material or a lithium cobalt oxide cathode material.

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