Preparation process of high-nickel ternary positive electrode sintering high-thermal-conductivity ceramic material

Abstract

This invention relates to the field of special ceramics preparation technology, and discloses a process for preparing high thermal conductivity ceramic materials for high-nickel ternary cathode sintering, including: preparing magnesium aluminum spinel green blanks containing magnesium oxide, yttrium oxide and titanium oxide composite additives; performing cyclic variable oxygen pressure sintering at 1420℃ to 1480℃, controlling the furnace atmosphere to periodically switch between the first and second oxygen partial pressure states. This invention utilizes the oxygen potential difference to drive the grain boundary liquid phase to alternate between low viscosity wetting and high viscosity pinning characteristics, eliminating the rheological quiescent zone at the end of sintering, effectively suppressing abnormal grain growth while ensuring high material density, and improving the thermal conductivity and lithium erosion resistance of the ceramic sagger.

Description

Technical Field

[0001] This invention belongs to the field of special ceramics preparation technology, and particularly relates to a preparation process of high thermal conductivity ceramic materials for high-nickel ternary cathode sintering. Background Technology

[0002] In the current industrial production system of lithium-ion battery cathode materials, magnesium-aluminum spinel ceramic saggers have become the core containers for high-nickel ternary materials to undergo high-temperature solid-state sintering due to their chemical stability. To meet the requirements of industrial production lines for sagger density and corrosion resistance, existing preparation processes generally adopt liquid-phase sintering technology, which introduces composite mineralizers such as yttrium oxide and titanium oxide into the raw material powder. These mineralizers react with matrix impurities at high temperatures to generate a low-melting-point liquid phase. The capillary pressure generated by the liquid phase wetting the particle surface promotes particle rearrangement and mass transfer, thereby achieving densification of the ceramic matrix.

[0003] However, as cathode materials evolve towards ultra-high nickel systems, sintering conditions impose more stringent physical constraints on the thermal conductivity and grain boundary stability of the saggar. In traditional static isothermal sintering, the densification process is limited by an inherent rheological attenuation mechanism. In the later stages of sintering, as the necks of ceramic particles grow and pore channels close, the capillary pressure driving the liquid phase flow decreases with increasing radius of curvature. Simultaneously, the high-temperature viscosity of the grain boundary liquid phase increases exponentially due to the dissolution of a large amount of matrix components. This physical contradiction between the attenuation of driving force and the surge in viscous resistance leads to the formation of unfillable rheological quiescent regions deep within the three-way grain boundaries where multiple grains converge. To address this rheological bottleneck, existing technologies attempt to forcibly promote the densification process through simple increases in sintering temperature or extended holding time, based on thermodynamics... The passive strategy of balance has shortcomings in practical applications. For example, Chinese invention patent CN1011229B discloses a method for synthesizing magnesium aluminum spinel. Although the scheme uses natural high-alumina bauxite and lightly calcined magnesium oxide, and obtains structural strength by calcining at an ultra-high temperature of 1650℃ to 1750℃, the extreme high temperature process is not suitable for high-nickel battery crucibles. On the one hand, the calcination temperature exceeding 1650℃ induces abnormal grain coarsening and excessive growth, resulting in a sharp reduction in the number of grain boundaries inside the material, which weakens the fracture toughness and thermal shock resistance of ceramics under frequent rapid cooling and heating conditions. On the other hand, under constant atmosphere and static temperature field, even if the viscosity of the liquid phase is reduced by high temperature, there is a lack of active flow physical potential energy to overcome the capillary resistance of deep closed pores. The remaining closed pores still become strong phonon scattering centers, making it difficult to break through the bottleneck of material thermal conductivity.

[0004] Therefore, the technical problem to be solved by this invention is how to establish a sintering process that can overcome rheological resistance, actively drive the liquid phase to fill deep grain boundaries, and control its crystal morphology. Summary of the Invention

[0005] This invention provides a process for preparing high thermal conductivity ceramic materials for high-nickel ternary cathode sintering, comprising the following steps:

[0006] Step 100: Prepare a multiphase ceramic green body by ball milling magnesium aluminum spinel matrix powder and composite sintering aid at a preset mass ratio, followed by spray granulation and pressing to obtain a ceramic green body; wherein, the composite sintering aid is composed of magnesium oxide, yttrium oxide and titanium oxide, and titanium oxide reacts with the matrix at the high sintering temperature to form a grain boundary liquid phase that is sensitive to oxygen partial pressure;

[0007] Step 200: Perform periodic variable oxygen pressure sintering treatment. Place the ceramic green body in an atmosphere-controlled furnace and perform densification sintering within a sintering temperature range of 1420℃ to 1480℃. During the densification sintering process, control the furnace atmosphere to cycle between a first atmosphere state and a second atmosphere state according to a preset sequence. The oxygen volume percentage in the first atmosphere state is higher than that in the second atmosphere state. In the first atmosphere state, the grain boundary liquid phase exhibits low viscosity wetting characteristics to fill pores. In the second atmosphere state, the grain boundary liquid phase exhibits high viscosity pinning characteristics to inhibit grain boundary migration. Through cyclic switching, the grain boundary liquid phase is driven to periodically permeate and flow and viscous blockage alternately within the grain boundary channels of the ceramic green body, thereby eliminating closed pores and inhibiting abnormal grain growth.

[0008] Preferably, in step 100, the amount of composite sintering aid added is 1.5% to 3.5% of the mass of magnesium aluminum spinel matrix powder; the composite sintering aid is composed of 15% to 25% magnesium oxide, 30% to 45% yttrium oxide and 30% to 55% titanium oxide by mass percentage; the composite sintering aid generates a grain boundary second phase with magnesium titanate and yttrium aluminum garnet as the main crystalline phases in situ during the sintering process.

[0009] Preferably, in step 200, the oxygen volume percentage in the first atmosphere state control furnace is 18% to 22%; the oxygen volume percentage in the second atmosphere state control furnace is 2% to 5%; the cycle switching includes 3 to 5 complete cycles, and the duration of each cycle is 30 to 60 minutes.

[0010] Preferably, before step 100, a pretreatment step of the magnesium aluminum spinel matrix powder is included: selecting the median diameter Magnesium aluminum spinel powder with a particle size of 2μm to 5μm was acid-washed to remove surface impurities and then calcined at 1200℃ to 1300℃ to eliminate lattice distortion stress.

[0011] Preferably, in step 200, the atmosphere switching parameters for each cycle are constrained by the oxygen potential adjustment factor Φ, and the formula for calculating the oxygen potential adjustment factor Φ is as follows: ,in, This represents the volume percentage of oxygen under the first atmospheric condition. This represents the volume percentage of oxygen under the second atmospheric condition. This represents the duration of maintaining the first atmospheric state within one cycle. The value representing the duration of maintaining the second atmosphere state within one cycle, with the oxygen potential adjustment factor Φ controlled between 8 and 15.

[0012] Preferably, after step 200, a step of stepped cooling is further included: controlling the furnace temperature to decrease to 1200°C at a rate of 2°C / min to 5°C / min, and maintaining this temperature at a constant temperature for 1 hour to 2 hours, and then allowing the furnace to cool naturally to room temperature; the step of stepped cooling is used to control the precipitation morphology of the second phase at the grain boundary, so that it forms a discontinuous island structure at the three-way grain boundary.

[0013] Preferably, in step 100, the pressing and molding adopts a cold isostatic pressing process, the molding pressure is 180MPa to 220MPa, and the holding time is 2 minutes to 5 minutes; before entering step 200, the ceramic green body undergoes constant temperature hot degreasing treatment at 300℃, 450℃ and 600℃ in an independent heating device.

[0014] Preferably, in step 200, the cycle switching is achieved by adjusting the flow ratio of oxygen to nitrogen entering the furnace through a gas mass flow controller; the gas mass flow controller is set to complete the replacement of the furnace atmosphere from the first atmosphere state to the second atmosphere state within 30 seconds while maintaining a constant total gas pressure inside the furnace.

[0015] Preferably, the titanium element in the composite sintering aid is enriched at the grain boundaries of the ceramic material after sintering, forming a titanium-containing grain boundary barrier layer. The grain boundary barrier layer is used to prevent lithium ions from diffusing into the ceramic matrix at high temperatures.

[0016] Preferably, the preparation process is used to manufacture a crucible that supports the positive electrode material of a high-nickel lithium battery. The crucible has a thermal conductivity greater than 15 W / (m·K) at 1000℃ and an apparent porosity of less than 1%.

[0017] Compared with existing technologies, the preparation process of high thermal conductivity ceramic materials for high-nickel ternary cathode sintering in this invention has the following advantages:

[0018] 1. In the preparation of high thermal conductivity ceramic materials, this invention breaks through the densification mechanism of static sintering rheological threshold. By constructing a process environment with periodic oscillation of oxygen partial pressure during the high-temperature sintering stage, and utilizing the reversible cyclic characteristics of the valence state of titanium element in the composite mineralizer under different oxygen potentials, a chemical potential-driven mechanism independent of capillary force is established inside the ceramic grain boundary liquid phase. During the alternating switching between oxygen-deficient and oxygen-rich atmospheres, the grain boundary liquid phase undergoes volume pulsation and viscosity oscillation due to the generation and disappearance of lattice oxygen vacancies, generating micro-hydrostatic pressure. This hydrostatic pressure overcomes the viscous resistance caused by neck growth and impurity dissolution in the later stage of sintering, driving the liquid phase to penetrate deep into the particle contact interface that cannot be wetted in the traditional static sintering process, and actively expelling the deep-seated stagnant gas. This mechanism effectively eliminates the rheological static zone at the three-way grain boundary, enabling the material to solve the technical contradiction between high densification and abnormal grain growth without relying on extreme sintering temperatures.

[0019] 2. Preferred Orientation of Grain Boundary Thermal Bridges and Reconstruction of Phonon Channels: This invention utilizes the coupling effect of flow shear stress and temperature gradient during the micro-pumping process of the liquid phase to induce the subsequent precipitation of grain boundary heat transfer phases to grow in preferred orientation along the heat flow direction. Unlike the disordered distribution of grain boundary phases in traditional processes, this textured grain boundary structure constructs phonon transport channels with low scattering cross-sections between ceramic matrix particles, reducing the interfacial thermal resistance when phonons cross grain boundaries. By transforming the disordered glassy barrier layer in situ into an ordered crystalline thermal bridge, this invention ensures that the ceramic material can maintain rapid and synchronized thermal flow response when facing the complex thermal field of high-nickel cathode material sintering conditions, effectively suppressing the temperature difference inside and outside the sagger and the corresponding thermal stress damage caused by thermal hysteresis.

[0020] 3. Based on the ion-selective blocking effect of lattice energy traps, this invention introduces specific rare earth element combinations into the composite mineralization system to construct a controlled asymmetric lattice distortion field in the in-situ generated grain boundary phase. This alters the local electron cloud density within the grain boundary phase, forming electrostatic trapping potential traps for ions of specific radii. When highly active lithium vapor attempts to diffuse along the grain boundary, these lattice energy traps strongly anchor the penetrating lithium ions, cutting off their continuous migration path within the grain boundary. This transforms the grain boundary's defense mode against lithium from passive physical blocking to active chemical trapping, preventing the thermal bridge structure collapse caused by lithium ions replacing elements in the grain boundary phase. This ensures the long-term structural stability and thermal performance retention of the material under ultra-high concentration lithium atmospheres. Attached Figure Description

[0021] Figure 1 This is a flowchart illustrating the preparation and variable oxygen pressure sintering process of the high thermal conductivity ceramic material for high-nickel ternary cathode sintering according to the present invention.

[0022] Figure 2This is a schematic diagram of the atmosphere switching logic and system principle for the periodic variable oxygen pressure sintering in the preparation process of this invention. Detailed Implementation

[0023] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0024] It should be noted that all directional and positional terms used in this invention, such as: up, down, left, right, front, back, vertical, horizontal, inner, outer, top, bottom, transverse, longitudinal, center, etc., are only used to explain the relative positional relationship and connection between components in a specific state (as shown in the accompanying drawings). They are only for the convenience of describing this invention and do not require that this invention be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention. In addition, the descriptions of "first," "second," etc., in this invention are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated.

[0025] In the description of this invention, unless otherwise explicitly specified and limited, the terms installation, connection, and linking should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections; they can refer to direct connections or indirect connections through an intermediate medium; they can refer to the internal communication between two components. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0026] In the description of this specification, references to the terms "an embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example, and the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0027] A process for preparing a high-nickel ternary cathode material with high thermal conductivity for sintering includes the following steps:

[0028] Step 100: Prepare a multiphase ceramic green body by ball milling magnesium aluminum spinel matrix powder and composite sintering aid at a preset mass ratio, followed by spray granulation and pressing to obtain a ceramic green body; wherein, the composite sintering aid is composed of magnesium oxide, yttrium oxide and titanium oxide, and titanium oxide reacts with the matrix at the high sintering temperature to form a grain boundary liquid phase that is sensitive to oxygen partial pressure;

[0029] Step 200: Perform periodic variable oxygen pressure sintering treatment. Place the ceramic green body in an atmosphere-controlled furnace and perform densification sintering within a sintering temperature range of 1420℃ to 1480℃. During the densification sintering process, control the furnace atmosphere to cycle between a first atmosphere state and a second atmosphere state according to a preset sequence. The oxygen volume percentage in the first atmosphere state is higher than that in the second atmosphere state. In the first atmosphere state, the grain boundary liquid phase exhibits low viscosity wetting characteristics to fill pores. In the second atmosphere state, the grain boundary liquid phase exhibits high viscosity pinning characteristics to inhibit grain boundary migration. Through cyclic switching, the grain boundary liquid phase is driven to periodically permeate and flow and viscous blockage alternately within the grain boundary channels of the ceramic green body, thereby eliminating closed pores and inhibiting abnormal grain growth.

[0030] Preferably, in step 100, the amount of composite sintering aid added is 1.5% to 3.5% of the mass of magnesium aluminum spinel matrix powder; the composite sintering aid is composed of 15% to 25% magnesium oxide, 30% to 45% yttrium oxide and 30% to 55% titanium oxide by mass percentage; the composite sintering aid generates a grain boundary second phase with magnesium titanate and yttrium aluminum garnet as the main crystalline phases in situ during the sintering process.

[0031] Preferably, in step 200, the oxygen volume percentage in the first atmosphere state control furnace is 18% to 22%; the oxygen volume percentage in the second atmosphere state control furnace is 2% to 5%; the cycle switching includes 3 to 5 complete cycles, and the duration of each cycle is 30 to 60 minutes.

[0032] Preferably, before step 100, a pretreatment step of the magnesium aluminum spinel matrix powder is included: selecting the median diameter Magnesium aluminum spinel powder with a particle size of 2μm to 5μm was acid-washed to remove surface impurities and then calcined at 1200℃ to 1300℃ to eliminate lattice distortion stress.

[0033] Preferably, in step 200, the atmosphere switching parameters for each cycle are constrained by the oxygen potential adjustment factor Φ, and the formula for calculating the oxygen potential adjustment factor Φ is as follows: ,in, This represents the volume percentage of oxygen under the first atmospheric condition. This represents the volume percentage of oxygen under the second atmospheric condition. This represents the duration of maintaining the first atmospheric state within one cycle. The value representing the duration of maintaining the second atmosphere state within one cycle, with the oxygen potential adjustment factor Φ controlled between 8 and 15.

[0034] Preferably, after step 200, a step of stepped cooling is further included: controlling the furnace temperature to decrease to 1200°C at a rate of 2°C / min to 5°C / min, and maintaining this temperature at a constant temperature for 1 hour to 2 hours, and then allowing the furnace to cool naturally to room temperature; the step of stepped cooling is used to control the precipitation morphology of the second phase at the grain boundary, so that it forms a discontinuous island structure at the three-way grain boundary.

[0035] Preferably, in step 100, the pressing and molding adopts a cold isostatic pressing process, the molding pressure is 180MPa to 220MPa, and the holding time is 2 minutes to 5 minutes; before entering step 200, the ceramic green body undergoes constant temperature hot degreasing treatment at 300℃, 450℃ and 600℃ in an independent heating device.

[0036] Preferably, in step 200, the cycle switching is achieved by adjusting the flow ratio of oxygen to nitrogen entering the furnace through a gas mass flow controller; the gas mass flow controller is set to complete the replacement of the furnace atmosphere from the first atmosphere state to the second atmosphere state within 30 seconds while maintaining a constant total gas pressure inside the furnace.

[0037] Preferably, the titanium element in the composite sintering aid is enriched at the grain boundaries of the ceramic material after sintering, forming a titanium-containing grain boundary barrier layer. The grain boundary barrier layer is used to prevent lithium ions from diffusing into the ceramic matrix at high temperatures.

[0038] Preferably, the preparation process is used to manufacture a crucible that supports the positive electrode material of a high-nickel lithium battery. The crucible has a thermal conductivity greater than 15 W / (m·K) at 1000℃ and an apparent porosity of less than 1%.

[0039] Example 1: In the large-scale industrial production of ceramic saggers for sintering high-nickel ternary cathode materials, the production line faces a physical contradiction between densification stagnation and abnormal grain growth in the later stages of sintering. When the magnesium-aluminum spinel matrix enters the late stage of sintering above 1420°C, as the neck of the ceramic particles grows and the pore channels close, the capillary pressure driving the liquid phase flow decreases with the increase of the radius of curvature. The grain boundary liquid phase, which dissolves matrix impurities, exhibits an exponentially increasing high-temperature viscosity under constant oxygen partial pressure. This shear difference between driving force and resistance leads to the formation of unfillable rheological quiescent regions deep in the three-way grain boundaries. If the viscosity is reduced simply by increasing the sintering temperature, grain coarsening will inevitably be induced, thereby weakening the fracture toughness of the sagger under frequent thermal cycling.

[0040] The preparation process of this invention introduces a composite sintering aid composed of magnesium oxide, yttrium oxide, and titanium oxide into the raw materials, and performs periodic variable oxygen pressure sintering treatment during the densification sintering stage at 1420°C to 1480°C. This establishes a microscopic pumping mechanism that utilizes the valence state fluctuations of titanium to break rheological deadlock. Under this mechanism, the furnace atmosphere is controlled to cycle between a first atmosphere state with an oxygen volume percentage of 18% to 22% and a second atmosphere state with an oxygen volume percentage of 2% to 5% for 3 to 5 cycles according to a preset time sequence. During the oxygen-deficient window period of the second atmosphere state, titanium ions in the grain boundary liquid phase undergo oxidation. Towards The in-situ reduction induces the generation of lattice oxygen vacancies, leading to a decrease in liquid phase viscosity. Combined with the hydrostatic pressure generated by the micro-volume expansion, in-situ high-temperature X-ray diffraction tests confirmed that the lattice volume expansion rate caused by the transformation of titanium ions from tetravalent to trivalent is 12.4%. The theoretical hydrostatic pressure generated by this volume change within the confined grain boundary channels is 16.5 MPa. This pressure value is greater than the 3.2 MPa capillary resistance calculated based on the critical radius of 0.5 μm pores. This pressure difference is used to force the liquid phase to overcome the capillary force limit and penetrate and fill the nanoscale gaps at the particle contact interface. During the oxygen-rich window period of the alternating first atmosphere, titanium ions are oxidized back to... The liquid phase viscosity instantly rebounds and transforms into a high-viscosity pinned phase. This dynamic viscosity oscillation based on oxygen potential difference physically decouples the synchronous relationship between densification and grain growth. This process ultimately eliminates internal closed pores in ceramic materials without relying on extreme high temperatures, and forms a titanium-containing grain boundary barrier layer and a grain boundary second phase with magnesium titanate and yttrium aluminum garnet as the main crystalline phases in situ at the grain boundaries. This microstructure built by dynamic sintering not only blocks the diffusion of lithium ions into the ceramic matrix at high temperatures, but also makes the thermal conductivity of the sagger at 1000℃ greater than 15 W / (m·K) and the apparent porosity less than 1%. Thus, while meeting the stringent requirements for chemical inertness of high-nickel cathode materials, the thermal shock spalling life of the material is improved through fine grain strengthening.

[0041] Example 2: In the performance verification test of magnesium-aluminum spinel ceramic saggers for high-nickel ternary cathode materials, a high-temperature sintering test platform with precise atmosphere control was established to verify the engineering effectiveness of the variable oxygen pressure sintering process proposed in this invention in solving the rheological deadlock problem at the end of sintering. An airtight high-temperature pusher kiln equipped with a zirconia oxygen sensor and a mass flow controller was selected. Its temperature control accuracy is ±1℃, and the oxygen partial pressure control response time is less than 30 seconds, which is sufficient to meet the process requirements for rapid switching of the furnace atmosphere. In periodic variable oxygen pressure sintering, the real-time switching of the furnace atmosphere is executed by a PID closed-loop control system linked with the zirconia oxygen sensor and the multi-channel gas mass flow controller. The system is set to detect the atmosphere switching timing signal and then wait 30 seconds. Inside, the nitrogen-oxygen flow ratio at the inlet and the variable frequency fan speed at the outlet are coordinated to complete the atmosphere replacement within the effective temperature zone of the furnace, and the oxygen partial pressure fluctuation is controlled in real time within the range of ±0.5% of the set value. Based on the fast response flow field control logic, the system eliminates the defect of uneven distribution of redox reaction along the radial direction of ceramic green body caused by gas diffusion lag effect in traditional static atmosphere sintering. This makes the periodic oscillation of liquid phase rheological characteristics occur synchronously from the surface to the inside during the sintering process of large-size industrial-grade saggers. In order to simulate the fluctuation of real industrial raw materials and impurity interference, the magnesium aluminum spinel matrix powder used in the experiment was deliberately kept with silicon oxide and calcium oxide impurities with a mass percentage of 0.05% to 0.1% to reproduce the working condition of industrial-grade raw materials forming a high-viscosity silicate liquid phase at high temperature.

[0042] In the raw material preparation stage, the median diameter is selected. Using 2.5 μm magnesium aluminum spinel powder as the matrix, a composite sintering aid with a mass percentage of 2.5% was introduced. The formulation of this composite sintering aid was precisely set according to the component-function correlation rule: 20% magnesium oxide (as a solid solution stabilizer), 35% yttrium oxide (as a grain boundary second phase precursor), and 45% titanium oxide (as a variable valence rheology modifier sensitive to oxygen partial pressure). The mixed powder was ball-milled, spray-granulated, and isostatically pressed to prepare standard-sized test samples. During the sintering process, the following engineering decision logic was implemented regarding the setting of the core process parameter, the atmosphere switching cycle: Considering that the penetration rate of the liquid phase in the grain boundary capillary is limited by viscous resistance, and that the valence state transformation of titanium ions needs to overcome the diffusion barrier of oxygen in the liquid phase, the holding time of each atmosphere state was set to 45 minutes to ensure that the oxidation / reduction reaction can penetrate to the core of the ceramic body, while avoiding excessive grain growth caused by prolonged single atmosphere. The experimental design included the present invention... A rigorous comparative system between the experimental group and the multidimensional control group was established to reveal the patterns of technical effects through changes in data gradients. Among them, the experimental group of the present invention (Group A) was subjected to the breathing dynamic sintering process of the present invention at a sintering temperature of 1460℃, that is, four complete cycles were switched between a first atmosphere state with an oxygen volume percentage of 20% and a second atmosphere state with an oxygen volume percentage of 3%. The partial missing control group (Group B) only removed the titanium oxide component in the composite sintering aid (replacing it with an equal amount of magnesium oxide), and the other conditions were completely the same as those of Group A, to verify the necessity of the titanium ion valence change mechanism. The process missing control group (Group C) retained the complete titanium-containing composite sintering aid, but maintained a constant oxygen-rich atmosphere with an oxygen volume percentage of 20% throughout the process at 1460℃, to verify the synergistic effect of dynamic atmosphere switching. The out-of-range control group (Group D) increased the sintering temperature to 1550℃ and maintained a constant atmosphere, to examine whether simply increasing the temperature (the traditional technical path) could achieve the same effect.

[0043] The data and microstructure characterization results generated during the experiment are as follows: In the first stage of density and porosity testing, the Archimedes displacement method was used to determine the apparent porosity of the sample group (Group A) of this invention, which decreased to 0.08% and the bulk density reached 3.56 g / cm³, approaching the theoretical density limit. In contrast, the apparent porosity of the partially missing control group (Group B) was 2.4%, indicating that without the participation of titanium ions, complete densification could not be achieved at 1460℃ using only magnesium yttrium additives. The apparent porosity of the process-missing control group (Group C) was 1.2%, indicating that although titanium was introduced, titanium ions remained stable under a constant oxygen-rich atmosphere. The high valence state failed to trigger a decrease in liquid phase viscosity, resulting in some closed pores being unable to drain. In the second stage of microstructure and grain size analysis, the cross-section after corrosion was observed using scanning electron microscopy (SEM). The sample group (Group A) of this invention exhibited a uniform equiaxed crystal structure with an average grain size ( The porosity of the controlled phase was controlled between 8 μm and 12 μm, and a titanium-containing second phase with a wetting angle of less than 30° was clearly observed at the three-point grain boundaries, confirming the effective penetration of the low-viscosity liquid phase. In stark contrast, although the porosity of the out-of-range control group (Group D) decreased to below 0.5%, its average grain size increased to over 45 μm, and abnormal grain growth was observed (the largest grain exceeded 80 μm). This coarse grain structure directly led to the deterioration of its thermal shock resistance in the third stage. In the thermal performance and corrosion resistance tests, the thermal diffusivity at 1000℃ was measured and the thermal conductivity was calculated using the laser scintillation method. The high-temperature thermal conductivity of the sample group (Group A) of this invention reached 16.8 W / (m·K), which is higher than the 12.5 W / (m·K) of the process-deficient control group (Group C). The physical reason for this is that Group A eliminated the micropores that act as phonon scattering centers through dynamic sintering and generated a continuous second phase mainly composed of magnesium titanate and yttrium aluminum garnet in situ at the grain boundaries. The lattice effectively blocked phonon scattering. Further, the samples were placed in molten lithium hydroxide for a 50-hour corrosion test. The mass loss rate of the sample group (Group A) was 0.15 mg / cm², while the mass loss rate of the out-of-range control group (Group D) was 1.8 mg / cm² due to coarse glass phase segregation at the grain boundaries. This confirms that the grain boundary phase formed by the in-situ reaction in this invention is chemically inert. Based on the above experimental data, within a specific temperature range of 1460℃, only the sample group of this invention achieved simultaneous high density (porosity less than 0.1%), fine-grained structure (grain size less than 15 μm), and high thermal conductivity (greater than 15 W / (m·K)). This result physically confirms that by in-situ oxidation-reduction cycling of titanium oxide under a variable oxygen pressure field, a viscosity oscillation mechanism was constructed in the grain boundary liquid phase. This overcame the rheological deadlock of capillary force and viscous resistance without increasing the sintering temperature, solving the engineering problem of the incompatibility between densification and grain growth control in traditional processes.

[0044] Example 3: In this example, which supplements the process with an in-depth technical appendix, the determination logic of the key parameters, atmosphere switching frequency and oxygen partial pressure gradient, in the breathing dynamic sintering process (which was not detailed in the previous examples) is explained in detail. A targeted explanation of the underlying principles and a description of the calibration procedure are provided, constructing a transparent mapping path from physical principles to engineering parameters. The physical basis for setting the oxygen partial pressure gradient in breathing dynamic sintering originates from thermodynamic calculations of the viscosity-temperature dependence of the grain boundary liquid phase under different oxygen potentials. In practical industrial applications, to accurately calibrate the optimal oxygen partial pressure gradient suitable for specific raw material systems (especially magnesium-aluminum spinel matrices with different impurity contents), the following standardized calibration procedure is performed: Multiple sets of materials with the same formulation but in different oxygen partial pressure rings are prepared. High-temperature rheological testing samples were tested using a high-temperature rotational viscometer at a constant temperature of 1460℃. The dynamic viscosity response curves of the samples were measured as the oxygen volume percentage changed from 0.1% to 25%. The experimental data showed that when the oxygen volume percentage was below 5%, the viscosity of the titanium-containing liquid phase exhibited a non-linear decreasing trend, and a rheological window that balanced low viscosity and chemical stability was reached in the range of 2% to 5%. Based on this measured data, the upper limit of oxygen content in the oxygen-deficient state was determined to be 5%, ensuring that the liquid phase has sufficient fluidity to fill the triple grain boundaries. At the same time, the lower limit of oxygen content in the oxygen-rich state was determined to be 18%, utilizing the high viscosity characteristics under high oxygen potential to achieve dynamic pinning of grain boundaries and prevent abnormal grain engulfment in the later stage of densification.

[0045] To determine the atmosphere switching frequency, a liquid-phase permeation-reaction hysteresis model was introduced as the theoretical core for parameter setting. This model indicates that the atmosphere switching cycle is longer than the diffusion equilibrium time of oxygen ions in the liquid phase and shorter than the incubation time for grain coarsening. To quantify this time window, a set of variable-cycle sintering verification experiments were designed. While keeping the total sintering time constant, the atmosphere switching cycles were set to 15 minutes, 30 minutes, 45 minutes, 60 minutes, and 90 minutes, respectively. Quantitative metallographic analysis of the microstructure of the sintered samples was performed, and the porosity and grain size distribution variance were extracted as key evaluation indicators. Experimental results show that when the cycle is less than 30 minutes, due to… Insufficient oxygen diffusion depth resulted in numerous unfilled micropores remaining in the sample core. When the cycle exceeded 60 minutes, the variance in grain size distribution increased, indicating abnormal local grain growth. Based on this, and combined with the Arrhenius equation's correction for the diffusion rate, the optimal switching cycle range of 30 to 60 minutes was determined for this process at 1460℃. This procedure transforms empirical time parameters into engineering constants based on kinetic constraints, ensuring the reproducibility of the process under different equipment and loading levels. Finally, a phase diagram-guided component locking strategy was constructed to address the microscopic synergistic mechanism of the ratio of magnesium oxide, yttrium oxide, and titanium oxide in the composite sintering aid. This was achieved by consulting… The ternary phase diagram and high-temperature wettability experimental data revealed the precise roles of each component at the microscopic level: magnesium oxide mainly acts as a solid solution stabilizer, suppressing the distortion of the spinel lattice during the valence change process; yttrium oxide reacts with titanium oxide at the grain boundaries to form a high-melting-point yttrium aluminum garnet (YAG) phase or yttrium titanate phase. These second-phase particles precipitate during cooling and anchor themselves to the grain boundaries, thus refining the grains; while titanium oxide acts as a rheological switch sensitive to oxygen partial pressure. When determining the specific proportions, a formula fine-tuning experiment was conducted with the goal of approximating the eutectic point. By adjusting the ratio of the three components, their mixing melting point was made slightly lower than the sintering temperature. The temperature range is 1420℃-1480℃, which is higher than the service temperature of high-nickel ternary materials. This allows the material to provide a liquid phase during sintering and transform into a solid framework during service. Experiments have shown that when the mass ratio of magnesium oxide, yttrium oxide, and titanium oxide is controlled within the range of (15-25):(30-45):(30-55), a liquid phase system with a specific wetting angle (<30°) and optimal chemical inertness at high temperatures can be formed at the grain boundaries. This ratio range is not arbitrarily chosen, but is the only solution based on the dual constraints of phase equilibrium thermodynamics and interfacial chemical kinetics, ensuring the structural stability and functional integrity of the material under extreme working conditions.

[0046] Example 4: In the defensive example used to verify the stability and compliance of the technical solution, an adaptive process window calibration procedure and an atmosphere uniformity calibration procedure were constructed to address the two potential risks that the aforementioned process may face in actual industrial deployment: raw material batch fluctuations and kiln atmosphere non-uniformity. Standardized engineering response strategies ensured the reproducibility and consistency of the technical solution under different production conditions. To address the potential shift in liquid phase rheological properties caused by raw material batch fluctuations, a rapid process window calibration process based on the differential curve of sintering shrinkage rate was established. Before each batch of new raw material is put into production, a small amount of powder is pressed into a standard cylindrical sample and placed in a thermal expansion instrument for constant-rate heating testing. The curve of linear shrinkage rate versus temperature is recorded. By performing first-order differential processing on this curve, the maximum shrinkage rate temperature representing the starting point of grain boundary liquid phase formation and particle rearrangement is extracted. If measured If the deviation from the reference value exceeds 10℃, the densification sintering temperature will be fine-tuned according to the preset compensation logic: when When the temperature is increased, the sintering temperature range is shifted upwards as a whole, with the upward shift being [missing value]. The deviation value is 0.8 times; otherwise, the sintering temperature range is reduced. This procedure ensures that the grain boundary liquid phase is always in the optimal rheological state, regardless of the fluctuation of the raw material activity, thus avoiding microstructural defects caused by over-burning or under-burning.

[0047] To address the potential oxygen partial pressure gradient issue within large industrial kilns, an atmosphere field uniformity calibration scheme based on a tracer sample array was developed. During kiln commissioning or periodic maintenance, several titanium dioxide standard samples, highly sensitive to oxygen partial pressure, were pre-placed within the kiln's effective temperature zone according to a three-dimensional grid distribution. After executing a standard cycle of breathing-type dynamic sintering, the samples were removed and their resistivity was measured. Since the conductivity of titanium dioxide exhibits a clear functional relationship with its non-stoichiometry (i.e., oxygen vacancy concentration), this functional relationship was pre-stored in the PID controller's memory unit in the form of a discrete lookup table. In the middle section: when the oxygen volume percentage is 20%, the resistivity of the standard sample is calibrated to 1050 Ω·cm; when the oxygen volume percentage drops to 3%, the resistivity drops to 120 Ω·cm; the values ​​in the middle range are calculated in real time using a two-point linear interpolation algorithm. By analyzing the spatial distribution map of the sample resistivity, the actual distribution field of oxygen partial pressure in the furnace can be inverted and deduced. If the resistivity deviation in a local area is found to exceed the threshold, the local gas flow field is corrected by adjusting the opening of the corresponding air inlet valve or the speed of the exhaust fan in that area until the resistivity deviation of all samples converges to within ±5%.

[0048] Example 5: In this example focusing on the reproduction of technical solutions and the solidification of standardized procedures, addressing the two major engineering challenges involved in the aforementioned process implementation—uniformity control of composite sintering aids and thermal stress management during sintering—a wet ball milling dispersibility calibration procedure and a segmented heating rate optimization procedure were constructed. By quantitatively calibrating key pretreatment and process control parameters, performance dispersion caused by operational differences was eliminated, ensuring the stability of the technical solution in different batches of production. To address the potential agglomeration problem of composite sintering aids in the magnesium-aluminum spinel matrix, a dispersibility calibration process based on laser particle size analysis and Zeta potential was established. In the ball milling mixing step for preparing multiphase ceramic green bodies, to determine the optimal ball milling time and dispersant dosage, the following standardized experiment was performed: A mixed slurry with a solid content of 40% was prepared, using ammonium polyacrylate (PAA-NH4) as the dispersant. During ball milling, samples were taken every 2 hours, and the particle size distribution of the slurry was measured using a laser particle size analyzer, while its Zeta potential was monitored simultaneously. The experimental results showed that as the ball milling time increased, the slurry's particle size distribution decreased. The zeta potential gradually decreases, while its absolute value first increases and then stabilizes. When the ball milling time reaches 12 hours and the dispersant addition is 0.8% of the powder mass, the slurry... The system was stabilized below 1.2 μm and the absolute value of the Zeta potential exceeded 40 mV, indicating that the system had reached the optimal dispersion stability. Based on this critical point, a ball milling time of 12 hours and a dispersant addition of 0.8% were determined as standard process parameters to ensure the uniform distribution of additives such as titanium oxide at the microscale, thereby avoiding abnormal grain growth caused by local enrichment.

[0049] To address microcrack defects that may be caused by thermal expansion coefficient mismatch during sintering, a segmented heating rate optimization procedure was developed. Considering the differences in thermal expansion behavior between the magnesium-aluminum spinel matrix and the in-situ generated grain boundary second phase, particularly during the debinding and pre-sintering stages from 600℃ to 900℃, and the rapid shrinkage stage from 1200℃ to 1400℃, differentiated heating rates were set. The dimensional change rate of the green blank during the heating process was monitored in real time using a thermal expansion meter to identify the temperature range where the maximum shrinkage rate occurred. Based on this, the heating curve was refined as follows: in the range from room temperature to 600℃, a rapid heating rate of 5℃ / min was used to improve efficiency; in the range from 600℃ to 900℃... In the ℃ range, the temperature was reduced to 2℃ / min to ensure sufficient discharge of organic matter without damaging the pore structure; in the 1200℃ to 1400℃ range, the temperature was controlled at 3℃ / min to alleviate the accumulation of internal stress during the densification process. This segmented heating strategy effectively reduced the sintering scrap rate to below 0.5%, verifying the engineering value of this procedure in improving yield and mechanical reliability. To ensure that the ceramic green body prepared by the spray granulation step in the preparation process of this invention has the gas permeability and pore uniformity required for the breathing dynamic sintering process, the hollow sphere effect that easily occurs during the granulation process and the resulting risk of local densification hindrance were addressed by implementing a droplet drying kinetic metric (…). The granulation process optimization procedure, constrained by temperature, controls the hot air inlet temperature of the spray drying tower within a low superheat range of 210℃ to 230℃. This, combined with the rheological properties of the slurry (high solids content, greater than 45% by mass) and low viscosity (less than 300 mPa·s), ensures that the solvent evaporation rate on the droplet surface is always lower than the solute diffusion rate towards the droplet center. <1), This thermodynamic boundary condition enables the atomized droplets to follow a solidification path that prioritizes volume shrinkage rather than surface crusting during the flight drying process, thereby obtaining solid spherical particles with a solidity of over 95% and uniform bulk density. After isostatic pressing, these solid particles can spontaneously construct a three-dimensional interconnected gas transport channel network with narrow pore size distribution inside the green body. As a physical breathing interface in the subsequent variable oxygen pressure sintering process, it ensures that the periodically changing oxygen partial pressure signal can be transmitted to the geometric core of the large-size sagger component at a rate that conforms to Fick's diffusion law, thereby eliminating the core performance degradation caused by atmosphere penetration lag.

[0050] The embodiments of this application have been described above with reference to the accompanying drawings. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. This application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit of this application and the scope of protection of this invention, and all of these forms are within the protection scope of this application.

Claims

1. A process for preparing a high-nickel ternary cathode sintering high thermal conductivity ceramic material, characterized in that, Includes the following steps: Step 100: Prepare a multiphase ceramic green body by ball milling magnesium aluminum spinel matrix powder and composite sintering aid at a preset mass ratio, followed by spray granulation and pressing to obtain a ceramic green body; wherein, the composite sintering aid is composed of magnesium oxide, yttrium oxide and titanium oxide, and titanium oxide reacts with the matrix at the high sintering temperature to form a grain boundary liquid phase that is sensitive to oxygen partial pressure; Step 200: Perform periodic variable oxygen pressure sintering treatment. Place the ceramic green body in an atmosphere-controlled furnace and perform densification sintering within a sintering temperature range of 1420℃ to 1480℃. During the densification sintering process, control the atmosphere in the furnace to cycle between a first atmosphere state and a second atmosphere state according to a preset sequence. The oxygen volume percentage in the first atmosphere state is higher than that in the second atmosphere state. In the first atmosphere state, the grain boundary liquid phase exhibits low viscosity wetting characteristics to fill pores. In the second atmosphere state, the grain boundary liquid phase exhibits high viscosity pinning characteristics to inhibit grain boundary migration. Through cyclic switching, the grain boundary liquid phase is driven to periodically permeate and flow and viscous blockage alternately within the grain boundary channels of the ceramic green body.

2. The preparation process of a high-nickel ternary cathode sintering high thermal conductivity ceramic material according to claim 1, characterized in that, In step 100, the amount of composite sintering aid added is 1.5% to 3.5% of the mass of magnesium aluminum spinel matrix powder; the composite sintering aid is composed of 15% to 25% magnesium oxide, 30% to 45% yttrium oxide and 30% to 55% titanium oxide by mass percentage; the composite sintering aid generates a grain boundary second phase with magnesium titanate and yttrium aluminum garnet as the main crystalline phases in situ during the sintering process.

3. The preparation process of a high-nickel ternary cathode sintering high thermal conductivity ceramic material according to claim 1, characterized in that, In step 200, the oxygen volume percentage in the first atmosphere state control furnace is 18% to 22%; the oxygen volume percentage in the second atmosphere state control furnace is 2% to 5%; the cycle switching includes 3 to 5 complete cycles, and the duration of each cycle is 30 to 60 minutes.

4. The preparation process of a high-nickel ternary cathode sintering high thermal conductivity ceramic material according to claim 1, characterized in that, Before step 100, a pretreatment step of the magnesium aluminum spinel matrix powder is also included: selecting the median diameter Magnesium aluminum spinel powder with a particle size of 2μm to 5μm was acid-washed to remove surface impurities and then calcined at 1200℃ to 1300℃.

5. The preparation process of a high-nickel ternary cathode sintering high thermal conductivity ceramic material according to claim 3, characterized in that, In step 200, the atmosphere switching parameters for each cycle are constrained by the oxygen potential adjustment factor Φ, which is calculated using the following formula: ,in, This represents the volume percentage of oxygen under the first atmospheric condition. This represents the volume percentage of oxygen under the second atmospheric condition. This represents the duration of maintaining the first atmospheric state within one cycle. The value representing the duration of maintaining the second atmosphere state within one cycle, with the oxygen potential adjustment factor Φ controlled between 8 and 15.

6. The preparation process of a high-nickel ternary cathode sintering high thermal conductivity ceramic material according to claim 1, characterized in that, After step 200, a step of stepped cooling is also included: the furnace temperature is controlled to decrease to 1200°C at a rate of 2°C / min to 5°C / min, and kept constant at this temperature for 1 to 2 hours, and then naturally cooled to room temperature with the furnace; the step of stepped cooling is used to control the precipitation morphology of the second phase at the grain boundary, so that it forms a discontinuous island structure at the three-way grain boundary.

7. The preparation process of a high-nickel ternary cathode sintering high thermal conductivity ceramic material according to claim 1, characterized in that, In step 100, the pressing and molding adopts a cold isostatic pressing process with a molding pressure of 180MPa to 220MPa and a holding time of 2 minutes to 5 minutes. Before entering step 200, the ceramic green body undergoes constant temperature hot degreasing treatment at 300℃, 450℃ and 600℃ in a separate heating device.

8. The preparation process of a high-nickel ternary cathode sintering high thermal conductivity ceramic material according to claim 1, characterized in that, In step 200, the cycle switching is achieved by adjusting the flow ratio of oxygen and nitrogen entering the furnace through a gas mass flow controller; the gas mass flow controller is set to complete the replacement of the furnace atmosphere from the first atmosphere state to the second atmosphere state within 30 seconds while maintaining a constant total gas pressure in the furnace.

9. The preparation process of a high-nickel ternary cathode sintering high thermal conductivity ceramic material according to claim 1, characterized in that, After sintering, the titanium element in the composite sintering aid is enriched at the grain boundaries of the ceramic material, forming a titanium-containing grain boundary barrier layer. The grain boundary barrier layer is used to prevent lithium ions from diffusing into the ceramic matrix at high temperatures.

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