A method for preparing a ceramic material for lithium battery separators

Abstract

A kind of preparation method of ceramic material for lithium battery separator, successively include the following steps: (1) preparation zirconium oxychloride solution, with ammonia water is neutralized and precipitated, control the pH value of reaction system is 8.6-9.0, generate zirconium hydroxide precursor;(2) to zirconium hydroxide precursor is washed by filter pressing, and zirconium hydroxide filter cake is prepared;(3) zirconium hydroxide filter cake is calcined, and the calcination temperature is 740-750 DEG C, generate zirconium dioxide granular material;(4) zirconium dioxide granular material is added water and made into slurry, add water-soluble anionic polymer, grind and remove magnetic inclusion, grind to particle size reaches 0.4-0.6 μm;(5) spray granulation;(6) secondary magnetic inclusion is removed;(7) airflow crushing.The method of the application can prepare ceramic powder with excellent dispersibility, uniform particle size and low magnetic inclusion, so that when it is used as lithium battery separator coating material, it can significantly improve the thermal stability of battery, and improve the electrolyte wettability and liquid retention capacity.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery separator technology, and specifically to a method for preparing ceramic materials for lithium battery separators. Background Technology

[0002] In the construction of lithium batteries, the separator plays a crucial role in ion conduction and must also isolate the positive and negative electrodes to prevent short circuits. Its performance directly affects the battery's cycle life and rate performance. Currently, mainstream polyolefin separators (such as polypropylene (PP) and polyethylene (PE)) have significant defects: PP has a melting point of 165℃, and PE has a melting point of 135℃. Under the high-temperature environment generated by battery operation, they are prone to shrinkage or melting, which can lead to internal short circuits, causing battery fires or even explosions, posing serious safety hazards.

[0003] To address the aforementioned issues, coating the surface of polyolefin separators with inorganic ceramic particles has become an effective and economical means to improve thermal stability. Ceramic materials, with their high heat resistance, can ensure the structural stability of the separator at high temperatures, and when combined with adhesives, they can maintain the overall structural integrity of the coating and the composite separator. However, existing ceramic coating materials face several challenges in their preparation: insufficient powder dispersibility, leading to uneven coating; wide particle size distribution, affecting separator porosity; residual magnetic impurities potentially causing micro-short circuits within the battery; and traditional preparation processes are complex and energy-intensive, making them unsuitable for large-scale industrial production. Therefore, developing a simple method for preparing ceramic materials for lithium-ion battery separators that produces materials with good dispersibility, uniform particle size, and low magnetic impurities is of significant practical importance. Summary of the Invention

[0004] The technical problem to be solved by this invention is to provide a method for preparing ceramic materials for lithium battery separators. This method can produce ceramic powders with excellent dispersibility, uniform particle size, and low magnetic inclusions. When used as a coating material for lithium battery separators, this powder can significantly improve the thermal stability of the battery and enhance electrolyte wettability and liquid retention, thereby improving battery performance and lifespan. The technical solution adopted is as follows: A method for preparing a ceramic material for a lithium battery separator, characterized by comprising the following steps in sequence: (1) Neutralization and precipitation to prepare zirconium hydroxide precursor Zirconium oxychloride was prepared by mixing zirconium oxychloride with industrial pure water at a mass ratio of 1:0.9-1.1. After filtration, the zirconium oxychloride solution was neutralized and precipitated with ammonia in an acid and alkali resistant reactor. During the reaction, the pH value of the reaction system was monitored and controlled in real time to be 8.6-9.0, and zirconium hydroxide precursor was generated. (2) Filter press washing The zirconium hydroxide precursor obtained in step (1) was subjected to pressure filtration and washing to obtain a zirconium hydroxide filter cake with a solid content >35% and a chloride content <400ppm. (3) Calcination phase transformation The zirconium hydroxide filter cake obtained in step (2) is calcined in a pusher furnace, and the calcination temperature is controlled at 740-750℃ to cause zirconium hydroxide to undergo phase transformation and generate zirconium dioxide granules. (4) Pulping and grinding The zirconium dioxide particles obtained in step (3) are mixed with water to form a slurry, and a water-soluble anionic polymer is added to the slurry. The slurry is then ground to remove magnetic inclusions during the grinding process until the particle size reaches 0.4-0.6 μm. (5) Spray granulation The slurry ground in step (4) is granulated by spray drying equipment to obtain granulated powder; (6) Secondary demagnetization inclusions Electromagnetic iron removal equipment is used to remove magnetic inclusions from granulated powder; (7) Airflow pulverization The granulated powder is fed into an air jet mill for air jet milling to obtain ceramic materials for lithium battery separators.

[0005] The final ceramic material for lithium-ion battery separators is a zirconium dioxide powder material suitable for coating lithium-ion battery separators. The specific surface area of ​​the obtained ceramic material for lithium-ion battery separators (i.e., zirconium dioxide powder) is 18-22 m² / g.

[0006] In preferred step (1), the ZrO2 content of zirconium oxychloride is >36%, the conductivity of industrial pure water is ≤5μs / cm, and the ammonia concentration is 8.5-8.8%.

[0007] In step (1), insoluble impurities are removed by filtration to obtain a clear zirconium oxychloride solution.

[0008] In preferred step (2), the method for pressure filtration washing of the zirconium hydroxide precursor (reaction product) obtained in step (1) is as follows: first, pressure filter the zirconium hydroxide precursor, then wash it with deionized water, and then pressure filter it again; the washing process is repeated multiple times (e.g., 2-4 times). The purpose of pressure filtration washing is to thoroughly remove impurity ions and residual inorganic salts.

[0009] In step (3), by controlling the calcination conditions to 740-750℃, the specific surface area of ​​the generated zirconium dioxide particles can usually reach 15-18m² / g. After subsequent grinding, spray granulation, and air jet milling, the specific surface area of ​​the resulting ceramic material for lithium battery separator (i.e., zirconium dioxide powder) is 18-22m² / g. The specific surface area within this range is beneficial to improving the electrolyte's liquid retention capacity (liquid retention rate can reach 90-110%) and high-temperature sintering resistance (no obvious sintering of the coating at 150℃ for 1h).

[0010] In preferred step (3), the zirconium hydroxide filter cake obtained in step (2) is placed in a quartz crucible and placed in a pusher furnace for calcination. The temperature inside the pusher furnace is controlled at 740-750℃ and kept at that temperature for 3-5 hours to obtain zirconium dioxide granules.

[0011] The preferred method for removing magnetic inclusions in the slurry in step (4) is: during the grinding process, the slurry is circulated through a permanent magnet separator to remove magnetic inclusions in the slurry.

[0012] In step (4), a water-soluble anionic polymer (such as sodium polyacrylate) is added to the slurry for surface modification. By adsorbing hydroxyl functional groups, a stable double-layer structure is formed on the particle surface, which can increase the particle surface potential, form steric hindrance, improve powder dispersibility, and enhance the suspension stability of the ceramic slurry. Preferably, in step (4), the water-soluble anionic polymer is sodium polyacrylate, and the amount of sodium polyacrylate added is 0.5-0.6% of the slurry mass.

[0013] In step (4), grinding until the particle size reaches 0.4-0.6μm can ensure that the coating thickness is uniform (which is beneficial for adapting to the diaphragm coating) and form a reasonable particle packing structure with moderate porosity, which is beneficial for electrolyte wetting.

[0014] In preferred step (5), the air inlet temperature of the spray drying equipment is controlled at 265°C and the air inlet speed is 40 m / s to ensure that the granulated powder has good flowability and loose density.

[0015] In step (6), the granulated powder is subjected to another demagnetization treatment by an electromagnetic iron removal device to further remove any possible residual magnetic impurities and ensure the high purity of the powder. During the grinding process in step (4), the slurry is circulated through a permanent magnet iron remover to remove magnetic impurities once, and then subjected to a second demagnetization treatment by an electromagnetic iron removal device after granulation, so that the magnetic impurities (metal impurities such as Fe, Ni, and Co) are controlled at <5ppm, eliminating the fatal hidden danger of battery separator (micro-short circuit between positive and negative electrodes).

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. Performance Advantages: The prepared zirconia ceramic powder exhibits excellent dispersibility (absolute zeta potential of the dispersion in water > 30 mV), uniform particle size (average particle size D50 of approximately 0.5 μm; narrow particle size distribution, D90 / D10 < 2.0), and low magnetic inclusions (iron content < 5 ppm). When coated onto a separator, it reduces the separator's thermal shrinkage rate (150℃ / 0.5h) to < 1% and the electrolyte absorption rate to > 180%, significantly improving the battery's thermal stability and cycle life. The narrow particle size distribution results in a more regular particle packing structure during the coating process, allowing for controllable coating porosity (35-45%) and increasing ionic conductivity to 10. -3 S / cm or higher.

[0017] 2. Process advantages: By precisely controlling various process parameters (such as neutralization precipitation pH value 8.8±0.2, calcination temperature 740-750℃, grinding particle size 0.4-0.6μm, etc.), the process is standardized and controllable. The process is simple, easy to operate, suitable for large-scale industrial production, and energy consumption is reduced by more than 20% compared with traditional processes.

[0018] This invention optimizes process parameters and procedures to prepare ceramic powders with excellent dispersibility, uniform particle size, and low magnetic inclusions. When used as a coating material for lithium battery separators, this powder can significantly improve the thermal stability of the battery, as well as the electrolyte wettability and liquid retention capacity, thereby improving battery performance and lifespan. At the same time, it simplifies the process and makes it feasible for industrial application. Detailed Implementation

[0019] Example 1: In this example, the preparation method of the ceramic material for lithium battery separator includes the following steps in sequence: (1) Neutralization and precipitation to prepare zirconium hydroxide precursor Zirconium oxychloride was prepared by mixing zirconium oxychloride with industrial pure water at a mass ratio of 1:1. After filtration, the zirconium oxychloride solution was neutralized and precipitated with ammonia in an acid and alkali resistant reactor (the reaction temperature was controlled at 25℃). During the reaction, the pH value of the reaction system was monitored and controlled in real time to be 8.8±0.1, and zirconium hydroxide precursor was generated. In this step (1), the ZrO2 content of zirconium oxychloride is 38%, the conductivity of industrial pure water is 4 μs / cm, and the ammonia concentration is 8.6%. In step (1), insoluble impurities are removed by filtration (filtered through a 0.22 μm microporous membrane) to obtain a clear zirconium oxychloride solution; (2) Filter press washing The zirconium hydroxide precursor obtained in step (1) was subjected to pressure filtration and washing to obtain a zirconium hydroxide filter cake with a solid content of 38% and a chloride content of 350 ppm. In step (2), the method for pressure filtration and washing of the zirconium hydroxide precursor (reaction product) obtained in step (1) is as follows: first, pressure filter the zirconium hydroxide precursor, then wash it with deionized water, and then pressure filter it again; the washing process is repeated 3 times. (3) Calcination phase transformation The zirconium hydroxide filter cake obtained in step (2) is calcined in a pusher furnace, and the calcination temperature is controlled at 740℃ to cause zirconium hydroxide to undergo phase transformation and generate zirconium dioxide granules. In step (3), the zirconium hydroxide filter cake obtained in step (2) is placed in a quartz crucible and placed in a pusher furnace for calcination. The temperature inside the pusher furnace is controlled at 740°C and kept at that temperature for 4 hours to obtain zirconium dioxide granules. (4) Pulping and grinding The zirconium dioxide particles obtained in step (3) are mixed with water to make a slurry (the zirconium dioxide particles and deionized water are mixed at a mass ratio of 1:2). A water-soluble anionic polymer (sodium polyacrylate is added to the slurry, the amount of sodium polyacrylate added is 0.5% of the slurry mass, and the molecular weight of sodium polyacrylate is 100,000) is then ground. During the grinding process, magnetic inclusions in the slurry are removed and the particles are ground until the particle size reaches 0.5 μm. The method for removing magnetic inclusions in the slurry in step (4) is as follows: during the grinding process, the slurry is circulated through a permanent magnet separator (magnetic field strength 1.2T) to remove magnetic inclusions in the slurry; (5) Spray granulation The slurry ground in step (4) is granulated by spray drying equipment to obtain granulated powder; In this step (5), the inlet air temperature of the spray drying equipment is controlled at 265℃, the inlet air velocity at 40m / s, and the outlet air temperature at 100℃. (6) Secondary demagnetization inclusions Electromagnetic iron removal equipment (magnetic field strength 1.5T) is used to remove magnetic inclusions from granulated powder; (7) Airflow pulverization The granulated powder was fed into an air jet mill for air jet milling (air jet milling pressure 0.8 MPa) to obtain ceramic material for lithium battery separators. The specific surface area of ​​the obtained ceramic material for lithium battery separators (i.e., zirconium dioxide powder) was 21 m² / g.

[0020] Example 2: In this example, the preparation method of the ceramic material for the lithium battery separator includes the following steps in sequence: (1) Neutralization and precipitation to prepare zirconium hydroxide precursor Zirconium oxychloride was prepared by mixing zirconium oxychloride with industrial pure water at a mass ratio of 1:1.1. After filtration, the zirconium oxychloride solution was neutralized and precipitated with ammonia in an acid and alkali resistant reactor (the reaction temperature was controlled at 30℃). During the reaction, the pH value of the reaction system was monitored and controlled in real time to be 8.7±0.1, and zirconium hydroxide precursor was generated. In this step (1), the ZrO2 content of zirconium oxychloride is 37%, the conductivity of industrial pure water is 4 μs / cm, and the ammonia concentration is 8.5%. In step (1), insoluble impurities are removed by filtration (filtered through a 0.22 μm microporous membrane) to obtain a clear zirconium oxychloride solution; (2) Filter press washing The zirconium hydroxide precursor obtained in step (1) was subjected to pressure filtration and washing to obtain a zirconium hydroxide filter cake with a solid content of 36% and a chloride content of 380 ppm. In step (2), the method for pressure filtration and washing of the zirconium hydroxide precursor (reaction product) obtained in step (1) is as follows: first, pressure filter the zirconium hydroxide precursor, then wash it with deionized water, and then pressure filter it again; the washing process is repeated 3 times. (3) Calcination phase transformation The zirconium hydroxide filter cake obtained in step (2) is calcined in a pusher furnace, and the calcination temperature is controlled at 750°C to cause zirconium hydroxide to undergo phase transformation and generate zirconium dioxide granules. In step (3), the zirconium hydroxide filter cake obtained in step (2) is placed in a quartz crucible and placed in a pusher furnace for calcination. The temperature inside the pusher furnace is controlled at 750°C and kept warm for 5 hours to obtain zirconium dioxide granules. (4) Pulping and grinding The zirconium dioxide particles obtained in step (3) are mixed with water to make a slurry (the zirconium dioxide particles and deionized water are mixed at a mass ratio of 1:2). A water-soluble anionic polymer (sodium polyacrylate is added to the slurry, the amount of sodium polyacrylate added is 0.6% of the slurry mass, and the molecular weight of sodium polyacrylate is 80,000) is then ground. During the grinding process, magnetic inclusions in the slurry are removed and the particles are ground until the particle size reaches 0.6 μm. The method for removing magnetic inclusions in the slurry in step (4) is as follows: during the grinding process, the slurry is circulated through a permanent magnet separator (magnetic field strength 1.2T) to remove magnetic inclusions in the slurry; (5) Spray granulation The slurry ground in step (4) is granulated by spray drying equipment to obtain granulated powder; In this step (5), the inlet air temperature of the spray drying equipment is controlled at 265℃, the inlet air velocity is 40m / s, and the outlet air temperature is 110℃. (6) Secondary demagnetization inclusions Electromagnetic iron removal equipment (magnetic field strength 1.5T) is used to remove magnetic inclusions from granulated powder; (7) Airflow pulverization The granulated powder was fed into an air jet mill for air jet milling (air jet milling pressure 0.7 MPa) to obtain a ceramic material for lithium battery separators. The specific surface area of ​​the obtained ceramic material for lithium battery separators (i.e., zirconium dioxide powder) was 19 m² / g.

[0021] The performance of the ceramic materials (i.e. zirconium dioxide powder) for lithium battery separators prepared in Examples 1-2 was tested, and the performance test results are shown in Table 1 below.

[0022] Table 1 Average particle size (D50, μm) 0.52 0.50 Particle size distribution (D90 / D10) 1.8 1.72 Specific surface area (m² / g) 21 19 Magnetic inclusion content (ppm) 3 4 Zeta potential of dispersion (mV) -35 -33 Dispersion Dispersion stability > 24h Dispersion stability > 24h Thermal shrinkage rate after diaphragm coating (150℃ / 0.5h) 0.8% 0.9% Electrolyte absorption rate 185% 182% <![CDATA[Ionic conductivity (10 -3 S / cm)]]> 1.2 1.1 Comparative Example 1 The preparation method of the ceramic material for the lithium battery separator in Comparative Example 1 is the same as that in Example 1, except that the calcination temperature in step (3) is changed to 700℃. The performance test results are shown in Table 2 below.

[0023] Table 2 <![CDATA[Specific surface area (m 2 / g)]]> 35.2 21.0 Zeta potential of dispersion (mV) -25.3 -35.0 Thermal shrinkage rate after diaphragm coating (150℃ / 0.5h) 2.3% 0.8% Electrolyte absorption rate 152% 185% Results analysis: The calcination temperature was too low (700℃), resulting in incomplete phase transformation of zirconium hydroxide, excessive residual hydroxyl groups, and an abnormally large specific surface area of ​​the powder. (1) Excessive surface hydroxyl groups enhance interparticle hydrogen bonding and reduce dispersibility (absolute value of zeta potential < 30mV). (2) During coating, the particles tend to agglomerate, resulting in a loose coating structure that cannot effectively prevent film shrinkage at high temperatures (heat shrinkage rate rises to 2.3%). (3) Agglomerated particles block the gaps in the coating, reduce the electrolyte wetting channels, and decrease the absorption rate by 33 percentage points.

[0024] Comparative Example 2 The preparation method of the ceramic material for the lithium battery separator in Comparative Example 2 is the same as that in Example 1, except that the calcination temperature in step (3) is changed to 720°C. The performance test results are shown in Table 3 below.

[0025] Table 3 <![CDATA[Specific surface area (m 2 / g)]]> 26.8 21.0 Zeta potential of dispersion (mV) -29.1 -35.0 Thermal shrinkage rate after diaphragm coating (150℃ / 0.5h) 1.5% 0.8% Electrolyte absorption rate 168% 185% Results analysis: The low calcination temperature (720℃) resulted in: (1) The zirconium hydroxide phase transformation was incomplete, and the specific surface area increased to 26.8 m². 2 / g, the hydroxyl groups on the particle surface increased slightly, and the dispersibility decreased slightly (zeta potential is close to the critical value of -30mV). (2) The coating has small agglomerates in some areas. The thermal shrinkage rate increased by 0.7 percentage points compared with Example 1, and the electrolyte absorption rate decreased by 17 percentage points. Although it is better than Comparative Example 1, it is not as good as Example 1.

[0026] Comparative Example 3 The preparation method of the ceramic material for the lithium battery separator in Comparative Example 3 is the same as that in Example 1, except that the calcination temperature in step (3) is changed to 760°C. The performance test results are shown in Table 4 below.

[0027] Table 4 <![CDATA[Specific surface area (m 2 / g)]]> 16.5 21.0 Zeta potential of dispersion (mV) -29.5 -35.0 Thermal shrinkage rate after diaphragm coating (150℃ / 0.5h) 1.4% 0.8% Electrolyte absorption rate 162% 185% Results analysis: The high calcination temperature (760℃) resulted in: (1) The particles were slightly sintered, and the specific surface area decreased to 16.5 m². 2 / g, surface activity decreased, and electrolyte absorption rate decreased by 23 percentage points; (2) The dispersion is slightly poor (zeta potential -29.5mV), the coating density is slightly reduced, and the thermal shrinkage rate increases to 1.4%. The performance is better than Comparative Example 4 but not as good as Example 1.

[0028] Comparative Example 4 The preparation method of the ceramic material for the lithium battery separator in Comparative Example 4 is the same as that in Example 1, except that the calcination temperature in step (3) is changed to 800℃. The performance test results are shown in Table 5 below.

[0029] Table 5 <![CDATA[Specific surface area (m 2 / g)]]> 8.6 21.0 Zeta potential of dispersion (mV) -28.7 -35.0 Thermal shrinkage rate after diaphragm coating (150℃ / 0.5h) 1.9% 0.8% Electrolyte absorption rate 145% 185% Results analysis: Excessive calcination temperature (800℃) caused over-sintering of zirconium dioxide particles, resulting in grain growth. (1) The specific surface area dropped sharply to 8.6 m² 2 / g, the number of active sites on the particle surface is reduced, the contact area with the electrolyte decreases, and the electrolyte absorption rate drops to 145%; (2) The hardness of sintered particles increases, the flowability of powder decreases after grinding, the uniformity of coating thickness decreases during coating, and the thermal shrinkage rate rises to 1.9% at high temperature; (3) The number of surface hydroxyl groups decreases, the stability of the double layer weakens, and the dispersibility decreases (absolute value of zeta potential < 30mV).

[0030] Comparative Example 5 The preparation method of the ceramic material for the lithium battery separator in Comparative Example 5 is the same as that in Example 1, except that the pH value of the neutralization and precipitation reaction system in step (1) is controlled at 8.0±0.1. The performance test results are shown in Table 6 below.

[0031] Table 6 Chloride content in filter cake (ppm) 580 350 Magnetic inclusion content (ppm) 7.5 3.0 Zeta potential of dispersion (mV) -22.1 -35.0 Thermal shrinkage rate after diaphragm coating (150℃ / 0.5h) 2.8% 0.8% Electrolyte absorption rate 138% 185% Results analysis: A pH value that is too low (8.0±0.1) leads to an incomplete neutralization reaction of zirconium oxychloride. (1) Residual chloride ions cannot be completely removed by washing (the chloride content of the filter cake after pressure filtration and washing is too high). Chloride ions will corrode the electrode plates and at the same time aggravate particle agglomeration and significantly reduce dispersibility (absolute value of zeta potential < 25mV). (2) Insufficient neutralization leaves unreacted zirconium oxychloride in the precursor, which generates chlorine-containing impurities after calcination and adsorbs magnetic particles (magnetic inclusions rise to 7.5 ppm), which can easily cause micro-short circuits in the battery. (3) Impurities and agglomerated particles in the coating destroy the structural integrity, the thermal shrinkage rate increases to 2.8%, and the electrolyte absorption rate decreases by 47 percentage points.

[0032] Comparative Example 6 The preparation method of the ceramic material for the lithium battery separator in Comparative Example 6 is the same as that in Example 1, except that the pH value of the neutralization and precipitation reaction system in step (1) is controlled at 8.4 ± 0.1. The performance test results are shown in Table 7 below.

[0033] Table 7 Chloride content in filter cake (ppm) 420 350 Magnetic inclusion content (ppm) 5.1 3.0 Zeta potential of dispersion (mV) -28.0 -35.0 Thermal shrinkage rate after diaphragm coating (150℃ / 0.5h) 1.6% 0.8% Electrolyte absorption rate 165% 185% Results analysis: A pH value that is too low can cause: (1) The neutralization reaction was nearly complete but trace amounts of chloride ions remained (420 ppm, slightly above the upper limit of 400 ppm), the adsorption of magnetic impurities increased (5.1 ppm), and the dispersibility decreased. (2) The coating uniformity decreased slightly, the thermal shrinkage rate increased by 0.8 percentage points, and the electrolyte absorption rate decreased by 20 percentage points. The performance was better than Comparative Example 5 but not as good as Example 1.

[0034] Comparative Example 7 The preparation method of the ceramic material for the lithium battery separator in Comparative Example 7 is the same as that in Example 1, except that the pH value of the neutralization and precipitation reaction system in step (1) is controlled at 9.2±0.1. The performance test results are shown in Table 8 below.

[0035] Table 8 Filter cake solid content (%) 33 38 <![CDATA[Apparent density of powder (g / cm 3 )]]> 0.48 0.55 Zeta potential of dispersion (mV) -29.5 -35.0 Thermal shrinkage rate after diaphragm coating (150℃ / 0.5h) 1.3% 0.8% Electrolyte absorption rate 170% 185% Results analysis: High pH level leads to: (1) Excessive ammonia water leads to a decrease in the solid content of the filter cake (down to 33%), a slight decrease in dispersibility, a slight decrease in loose packing density, and an increase in drying energy consumption of about 10%; (2) The coating structure is slightly loose, the thermal shrinkage rate increases by 0.5 percentage points, and the electrolyte absorption rate decreases by 15 percentage points. The performance is better than Comparative Example 8 but not as good as Example 1.

[0036] Comparative Example 8 The preparation method of the ceramic material for the lithium battery separator in Comparative Example 8 is the same as that in Example 1, except that the pH value of the neutralization and precipitation reaction system in step (1) is controlled at 9.5±0.1. The performance test results are shown in Table 9 below.

[0037] Table 9 Filter cake solid content (%) 28 38 <![CDATA[Apparent density of powder (g / cm 3 ).]]> 0.32 0.55 Zeta potential of dispersion (mV) -26.5 -35.0 Thermal shrinkage rate after diaphragm coating (150℃ / 0.5h) 2.1% 0.8% Electrolyte absorption rate 148% 185% Results analysis: Excessive pH value leads to excessive ammonia: (1) Excess ammonia water causes a large amount of NH4+ to be adsorbed on the surface of zirconium hydroxide colloidal particles. 4+ This hinders particle aggregation, reduces the solid content of the filter cake (to 28%), and increases the energy consumption of subsequent spray drying by 30%. (2) NH 4+ Residual damage to the surface double layer of particles leads to instability, decreased dispersibility (absolute value of zeta potential < 30mV), reduced loose density of powder, and easy occurrence of pinholes in the coating during coating. (3) The coating structure is loose, and its anti-shrinkage ability is weakened at high temperature (heat shrinkage rate 2.1%), and the electrolyte retention capacity is reduced (electrolyte absorption rate 148%).

[0038] Comparative Example 9 The preparation method of the ceramic material for the lithium battery separator in Comparative Example 9 is the same as that in Example 1, except that step (4) is ground to a particle size of 0.2 μm. The performance test results are shown in Table 10 below.

[0039] Table 10 Particle size distribution (D90 / D10) 2.5 1.8 Dispersion stability (h) 8 ＞24 Porosity of diaphragm coating (%) 28 42 Electrolyte absorption rate 132% 185% <![CDATA[Ionic conductivity (10 -3 S / cm)]]> 0.85 1.2 Results analysis: Too small a grinding particle size (0.2μm) results in: (1) The specific surface area of ​​the particles increases sharply, the surface energy increases, and they are prone to agglomeration (particle size distribution D90 / D10>2.0), and the dispersion stability drops to 8 hours (far below 24 hours). (2) Agglomerated particles clog the coating pores, reducing the porosity to 28%, reducing the electrolyte wetting channels, and decreasing the electrolyte absorption rate to 132%; (3) Insufficient porosity leads to Li + As transport resistance increases, ionic conductivity decreases to 0.85 × 10⁻⁶. -3 S / cm, battery rate performance decreases.

[0040] Comparative Example 10 The preparation method of the ceramic material for the lithium battery separator in Comparative Example 10 is the same as that in Example 1, except that step (4) is ground to a particle size of 0.3 μm. The performance test results are shown in Table 11 below.

[0041] Table 11 Particle size distribution (D90 / D10) 2.1 1.8 Dispersion stability (h) 16 ＞24 Porosity of diaphragm coating (%) 35 42 Electrolyte absorption rate 160% 185% <![CDATA[Ionic conductivity (10 -3 S / cm)]]> 0.9 1.2 Results analysis: Too small a grinding particle size leads to: (1) The surface energy of the particles is slightly high, and there is slight agglomeration (D90 / D10=2.1), and the dispersion stability drops to 16 hours; (2) The coating porosity decreased to 35%, and the electrolyte absorption rate decreased by 25 percentage points. The performance was better than that of Comparative Example 9 but not as good as that of Example 1.

[0042] Comparative Example 11 The preparation method of the ceramic material for the lithium battery separator in Comparative Example 11 is the same as that in Example 1, except that step (4) is ground to a particle size of 0.7 μm. The performance test results are shown in Table 12 below.

[0043] Table 12 Diaphragm coating thickness uniformity (deviation %) 9 5 Coating adhesion (N / cm) 4.5 5.8 Thermal shrinkage rate after diaphragm coating (150℃ / 0.5h) 1.6% 0.8% Electrolyte absorption rate 172% 185% 3. Effect Analysis Too large a grinding particle size leads to: (1) The uniformity of particle packing decreased, the coating thickness deviation increased (up to 9%), and the coating adhesion decreased (down to 4.5 N / cm). (2) The thermal shrinkage rate increased by 0.8 percentage points and the electrolyte absorption rate decreased by 13 percentage points. The performance was better than Comparative Example 12 but not as good as Example 1.

[0044] Comparative Example 12 The preparation method of the ceramic material for the lithium battery separator in Comparative Example 12 is the same as that in Example 1, except that step (4) is ground to a particle size of 0.9 μm. The performance test results are shown in Table 13 below.

[0045] Table 13 Diaphragm coating thickness uniformity (deviation %) 15 5 Thermal shrinkage rate after diaphragm coating (150℃ / 0.5h) 2.5% 0.8% Coating adhesion (N / cm) 3.2 5.8 Electrolyte absorption rate 155% 185% Results analysis: Excessively large grinding particles lead to: (1) The particles cannot be precisely stacked, and the coating thickness deviation rises to 15% (far exceeding the allowable range of 5%). The local coating is too thin and is prone to shrinkage at high temperature (heat shrinkage rate 2.5%). (2) The contact area between large particles and the membrane substrate is reduced, the coating adhesion is reduced (down to 3.2 N / cm), and the coating is easy to fall off during charging and discharging; (3) If the gaps between particles are too large, the electrolyte's ability to retain liquid will decrease (absorption rate 155%), and the battery cycle life will be shortened by more than 20%.

[0046] Verification using Comparative Examples 1-12 above shows that only when the core process parameters, such as the pH value of the neutralization and precipitation reaction system in step (1), the calcination temperature in step (3), and the grinding particle size in step (4), are controlled within a suitable range (pH value of the neutralization and precipitation reaction system is 8.6-9.0, calcination temperature is 740-750℃, and grinding to a particle size of 0.4-0.6μm), can ceramic materials for lithium battery separators with good dispersibility, low magnetic inclusions, and excellent coating performance be prepared. If the process parameters deviate, the product performance will decline, failing to meet the safety and lifespan requirements of lithium batteries.

[0047] The test methods for each performance index in the above embodiments and comparative examples are shown in Table 14 below.

[0048] Average particle size (D50), particle size distribution (D90 / D10) According to GB / T 19077-2016 Particle Size Analysis by Laser Diffraction Specific surface area According to GB / T 19587-2017 "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method" Magnetic inclusion content According to GB / T 30454-2013 "Determination of Impurity Content in Lithium-ion Battery Materials - Inductively Coupled Plasma Atomic Emission Spectrometry" Zeta potential of dispersion According to GB / T 30431-2013 Determination of zeta potential of suspension systems by electrophoretic light scattering method Dispersion stability The static sedimentation method is operated as follows: 1. Prepare 100ml of 20wt% ceramic slurry and disperse it ultrasonically for 10min; 2. Place the slurry in a 25℃ constant temperature water bath and let it stand; 3. Observe the stratification every 2 hours and record the time when the height of the upper clear liquid is ≥5ml for the first time, which is the dispersion stabilization time. Thermal shrinkage rate after diaphragm coating According to GB / T 12027-2017 Test Method for Dimensional Change Rate of Plastic Films and Sheets under Heat Electrolyte absorption rate <![CDATA[The weighing method has the following operating steps: 1. Take a coated diaphragm of 10 cm × 10 cm, dry it at 105°C for 2 h until constant weight, and weigh the dry weight m1; 2. Immerse the sample in an electrolyte with EC:DMC = 1:1 (volume ratio) and let it stand at 25°C for 2 h; 3. After taking it out, absorb the remaining liquid on the surface and weigh the wet weight m2; 4. Calculate the electrolyte absorption rate, electrolyte absorption rate = (m2 - m1) / m1 × 100%. Among them, EC is ethylene carbonate and DMC is dimethyl carbonate.]]> Ionic conductivity According to GB / T 36672-2018 Determination of Conductivity of Electrolyte for Lithium-ion Batteries Diaphragm coating porosity According to GB / T 21650.2-2011 "Determination of Pore Size Distribution and Porosity of Solid Materials by Mercury Intrusion Porosimetry and Gas Adsorption Methods - Part 2: Gas Adsorption Method" Coating thickness uniformity (deviation %) According to GB / T6462-2005 "Microscopic Method for Measuring the Thickness of Metallic and Oxide Coatings" Coating adhesion According to GB / T2792-2014 Test Method for Peel Strength of Adhesive Tapes

Claims

1. A method for preparing a ceramic material for lithium battery separators, characterized in that... The steps are as follows: (1) Neutralization and precipitation to prepare zirconium hydroxide precursor Zirconium oxychloride was prepared by mixing zirconium oxychloride with industrial pure water at a mass ratio of 1:0.9-1.

1. After filtration, the zirconium oxychloride solution was neutralized and precipitated with ammonia in an acid and alkali resistant reactor. During the reaction, the pH value of the reaction system was monitored and controlled in real time to 8.7-8.8, and zirconium hydroxide precursor was generated. (2) Filter press washing The zirconium hydroxide precursor obtained in step (1) was subjected to pressure filtration and washing to obtain a zirconium hydroxide filter cake with a solid content >35% and a chloride content <400ppm. (3) Calcination phase transformation The zirconium hydroxide filter cake obtained in step (2) is calcined in a pusher furnace, and the calcination temperature is controlled at 740-750℃ to cause zirconium hydroxide to undergo phase transformation and generate zirconium dioxide granules. (4) Pulping and grinding The zirconium dioxide particles obtained in step (3) are mixed with water to form a slurry, and a water-soluble anionic polymer is added to the slurry. The slurry is then ground to remove magnetic inclusions during the grinding process until the particle size reaches 0.5-0.6 μm. The water-soluble anionic polymer is sodium polyacrylate, and the amount of sodium polyacrylate added is 0.5-0.6% of the slurry mass. The method for removing magnetic inclusions from slurry is as follows: during the grinding process, the slurry is circulated through a permanent magnet separator to remove magnetic inclusions from the slurry. (5) Spray granulation The slurry ground in step (4) is granulated by spray drying equipment to obtain granulated powder; (6) Secondary demagnetization inclusions Electromagnetic iron removal equipment is used to remove magnetic inclusions from granulated powder; (7) Airflow pulverization The granulated powder is fed into an air jet mill for air jet milling to obtain ceramic materials for lithium battery separators.

2. The method for preparing ceramic materials for lithium battery separators according to claim 1, characterized in that: In step (1), the ZrO2 content of zirconium oxychloride is >36%, the conductivity of industrial pure water is ≤5μs / cm, and the concentration of ammonia water is 8.5-8.8%.

3. The method for preparing ceramic materials for lithium battery separators according to claim 1, characterized in that: In step (1), insoluble impurities are removed by filtration to obtain a clear zirconium oxychloride solution.

4. The method for preparing ceramic materials for lithium battery separators according to claim 1, characterized in that: In step (2), the method for pressure filtration and washing of the zirconium hydroxide precursor obtained in step (1) is as follows: first, pressure filter the zirconium hydroxide precursor, then wash it with deionized water, and then pressure filter it again; the washing process is repeated multiple times.

5. The method for preparing ceramic materials for lithium battery separators according to claim 4, characterized in that: In step (2), the washing process is repeated 2-4 times.

6. The method for preparing ceramic materials for lithium battery separators according to claim 1, characterized in that: In step (3), the zirconium hydroxide filter cake obtained in step (2) is placed in a quartz crucible and placed in a pusher furnace for calcination. The temperature inside the pusher furnace is controlled at 740-750℃ and kept at that temperature for 3-5 hours to obtain zirconium dioxide granules.

7. The method for preparing ceramic materials for lithium battery separators according to claim 1, characterized in that: In step (5), the air inlet temperature of the spray drying equipment is controlled at 265℃ and the air inlet velocity is controlled at 40m / s.