Preparation method of sphere-like superfine boehmite

Abstract

The invention relates to a preparation method of sphere-like superfine boehmite, and belongs to the technical field of materials. According to the method, accurate control over the morphology and the particle size of boehmite is achieved through the two-step hydrothermal reaction of'first acid and second alkali ', the first hydrothermal reaction controls oriented growth of boehmite under induction of boehmite seed crystals, and a spheroidic boehmite prototype is formed; in the second hydrothermal reaction, the boehmite precursor obtained by the first hydrothermal reaction is deeply modified in an alkaline environment, and the boehmite is regularized into a sphere-like shape. The boehmite prepared by the method has high purity, ultrafine particle size and regular sphere-like morphology, and is especially suitable for being used as a coating material and a high-end precision polishing material of a high-end lithium battery ultrathin diaphragm.

Description

Technical Field

[0001] This application relates to the field of materials technology, and in particular to a method for preparing near-spherical ultrafine boehmite. Background Technology

[0002] Boehmite (γ-AlOOH), as a key inorganic material, plays an indispensable role in many industrial fields due to its unique physicochemical properties, such as high hardness, excellent thermal stability, good insulation properties, and high chemical inertness. Specifically, boehmite is widely used in catalyst supports, high-performance ceramic materials, surface protective coatings, lithium-ion battery separator coatings, and precision polishing materials.

[0003] However, current industrial-scale preparation methods for boehmite mainly rely on hydrothermal methods, but traditional one-step hydrothermal methods often struggle to simultaneously and precisely control the particle size, morphology, and purity of the product. In particular, the direct hydrothermal method using aluminum hydroxide as a raw material cannot meet the stringent requirements for material properties in ultra-thin diaphragm coating and high-end precision polishing. Summary of the Invention

[0004] This application provides a method for preparing near-spherical ultrafine boehmite to solve the following technical problem: how to simultaneously achieve precise control over the particle size, morphology and purity of boehmite. This application provides a method for preparing near-spherical ultrafine boehmite, the method comprising: Industrial-grade aluminum hydroxide is mixed with deionized water to obtain a slurry; An acidic regulator is added to the slurry to adjust the pH value of the slurry to a set range, thereby obtaining an acidic mixed slurry; Boehmite seed crystals are added to the acidic mixed slurry to induce directional nucleation and growth of boehmite, thereby obtaining an acidic mixed slurry containing seed crystals. The seed-containing acidic mixed slurry is subjected to a first hydrothermal reaction to achieve the initial formation and morphology control of boehmite, resulting in a first reaction slurry. An alkaline regulator is added to the first reaction slurry to adjust the pH value of the first reaction slurry, thereby obtaining an alkaline mixed slurry; The alkaline mixed slurry is subjected to a second hydrothermal reaction to achieve regularization of boehmite morphology and improvement of purity, thereby obtaining a second reaction slurry. The second reaction slurry was subjected to solid-liquid separation, washing, drying and pulverizing in sequence to obtain spherical ultrafine boehmite.

[0005] Optionally, the mass fraction of aluminum hydroxide in the slurry is 5% to 20%.

[0006] Optionally, the temperature of the first hydrothermal reaction is 190℃~220℃, and the time of the first hydrothermal reaction is 2h~8h.

[0007] Optionally, the temperature of the second hydrothermal reaction is 150℃~180℃, and the time of the second hydrothermal reaction is 4h~12h.

[0008] Optionally, the acidity regulator is at least one of nitric acid, hydrochloric acid, sulfuric acid, formic acid, acetic acid, oxalic acid, and citric acid.

[0009] Optionally, the alkalinity regulator is at least one of sodium hydroxide, potassium hydroxide, and ammonia water.

[0010] Optionally, the pH value of the acidic mixed slurry is 4 to 6.

[0011] Optionally, the pH value of the alkaline mixed slurry is 10 to 13.

[0012] Optionally, the D50 particle size of the boehmite seed crystal is <0.2μm, and the mass of the boehmite seed crystal is 1% to 10% of the mass of the industrial-grade aluminum hydroxide.

[0013] Optionally, the spheroidal ultrafine boehmite has a crystal structure of γ-AlOOH and possesses the following properties: Its microscopic morphology is spherical; The particle size distribution satisfies: D50 < 0.4 μm, D90 < 1.0 μm; Chemical purity >99.95wt%.

[0014] The technical solutions provided in this application have the following advantages compared with the prior art: This application provides a method for preparing near-spherical ultrafine boehmite. The method includes: mixing industrial-grade aluminum hydroxide with deionized water to obtain a slurry; adding an acidic regulator to the slurry to adjust its pH value to a set range to obtain an acidic mixed slurry; adding boehmite seed crystals to the acidic mixed slurry to induce directional nucleation and growth of boehmite to obtain a seed-containing acidic mixed slurry; subjecting the seed-containing acidic mixed slurry to a first hydrothermal reaction to achieve preliminary boehmite formation and morphology control to obtain a first reaction slurry; adding an alkaline regulator to the first reaction slurry to adjust its pH value to obtain an alkaline mixed slurry; subjecting the alkaline mixed slurry to a second hydrothermal reaction to achieve regularization of boehmite morphology and improvement of purity to obtain a second reaction slurry; and sequentially performing solid-liquid separation, washing, drying, and pulverizing on the second reaction slurry to obtain near-spherical ultrafine boehmite.

[0015] This application employs a two-step hydrothermal method. First, in an acidic environment, boehmite seed crystals induce boehmite nucleation and directional growth, forming a near-spherical boehmite precursor. Then, in an alkaline environment, the boehmite precursor obtained from the first hydrothermal reaction is deeply modified, resulting in smoother and more regular boehmite particle morphology, ultimately forming an ideal near-spherical structure. This also results in finer and more uniformly distributed boehmite particles, improving purity. Under acidic conditions (pH 4–6), industrial-grade aluminum hydroxide dissolves to form aluminate ions, providing the necessary chemical environment for boehmite formation. By adding ultrafine boehmite seed crystals (D50 < 0.2 μm) to the acidic mixed slurry as heterogeneous nucleation sites, boehmite preferentially grows epitaxially on the surface of the boehmite seed crystals, avoiding the problem of uneven boehmite particle size caused by homogeneous nucleation. Acidic conditions also inhibit the anisotropic growth of boehmite crystals, promoting uniform growth in all directions and laying the foundation for the formation of spherical boehmite structures. By adding an alkaline regulator to the first reaction slurry, the pH value of the slurry is precisely adjusted to 10–13, creating a strongly alkaline environment. This strongly alkaline condition "ripens" and "etches-recrystallizes" the boehmite precursor obtained from the first hydrothermal reaction, dissolving irregular small grains and sharp edges in the boehmite, reducing the surface energy of the boehmite particles, and making their morphology smoother and more regular. The alkaline environment also helps to wash away some soluble impurities in the boehmite, such as Fe and Na, thus purifying the boehmite and meeting the stringent purity requirements of high-end applications. The boehmite prepared by the two-step hydrothermal method has high purity, ultrafine particle size, and regular spherical morphology, making it particularly suitable as a coating material for ultra-thin separators in high-end lithium batteries and a high-precision polishing material. Attached Figure Description The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0016] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 XRD pattern of spheroidal ultrafine boehmite provided in Embodiment 1 of this application; Figure 2 This is a particle size diagram of the near-spherical ultrafine boehmite provided in Embodiment 1 of this application; Figure 3 SEM image of the near-spherical ultrafine boehmite provided in Embodiment 1 of this application; Figure 4SEM image of the spheroidal ultrafine boehmite provided in Comparative Example 1 of this application. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0019] The range descriptions used herein, such as numerical ranges and proportional ranges, include all possible sub-ranges and single numerical values ​​within that range. For example, the range descriptions of "1 to 6" or "1~6" cover all sub-ranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms "including" and "contains" as used herein mean "including but not limited to"; relational terms such as "first" and "second" are used only to distinguish different entities or operations and do not imply an actual order or relationship; "and / or" indicates that multiple situations can exist individually or simultaneously; expressions such as "at least one," "multiple," and "at least one" refer to any combination of the corresponding objects, including combinations of single or multiple objects. The proportional relationships mentioned herein, such as mass ratios and molar ratios, should be understood as the correspondence between the first and second terms of a proportional formula, according to the order of description. The raw materials, reagents, instruments, and equipment used herein can all be obtained through commercial purchase or prepared using existing methods.

[0020] This application provides a method for preparing near-spherical ultrafine boehmite, the method comprising: Industrial-grade aluminum hydroxide is mixed with deionized water to obtain a slurry; An acidic regulator is added to the slurry to adjust the pH value of the slurry to a set range, thereby obtaining an acidic mixed slurry; Boehmite seed crystals are added to the acidic mixed slurry to induce directional nucleation and growth of boehmite, thereby obtaining an acidic mixed slurry containing seed crystals. The seed-containing acidic mixed slurry is subjected to a first hydrothermal reaction to achieve the initial formation and morphology control of boehmite, resulting in a first reaction slurry. An alkaline regulator is added to the first reaction slurry to adjust the pH value of the first reaction slurry, thereby obtaining an alkaline mixed slurry; The alkaline mixed slurry is subjected to a second hydrothermal reaction to achieve regularization of boehmite morphology and improvement of purity, thereby obtaining a second reaction slurry. The second reaction slurry was subjected to solid-liquid separation, washing, drying and pulverizing in sequence to obtain spherical ultrafine boehmite.

[0021] This application provides a method for preparing near-spherical ultrafine boehmite. This method precisely controls the morphology, particle size, and purity of the boehmite through a two-step hydrothermal reaction, making it particularly suitable for high-end lithium battery separator coating and precision polishing. The industrial-grade aluminum hydroxide used in this application has a purity ≥98% and a D50 of 50 μm to 70 μm.

[0022] In some embodiments, the mass fraction of aluminum hydroxide in the slurry is 5% to 20%.

[0023] The dissolution of aluminum hydroxide in an acidic environment is a crucial step in the formation of aluminate ions. Setting the mass fraction of aluminum hydroxide in the slurry to 5%–20% ensures sufficient aluminum hydroxide dissolution, forming a adequate concentration of aluminate ions, providing ample raw materials for the subsequent formation of boehmite. Secondly, a mass fraction of 5%–20% aluminum hydroxide in the slurry helps control the purity and morphology of spheroidal ultrafine boehmite. A mass fraction below 5% may lead to incomplete reaction and low yield of spheroidal ultrafine boehmite; while a mass fraction above 20% may cause boehmite particle agglomeration, affecting the dispersibility and morphological uniformity of the spheroidal ultrafine boehmite. For example, the mass fraction of aluminum hydroxide in the slurry can be 5%, 8%, 11%, 14%, 17%, 20%, etc.

[0024] In some embodiments, the acidity regulator is at least one selected from nitric acid, hydrochloric acid, sulfuric acid, formic acid, acetic acid, oxalic acid, and citric acid.

[0025] In the preparation of near-spherical ultrafine boehmite, adding an acidic regulator to the slurry can adjust its pH to a suitable range, creating an acidic environment conducive to the directional nucleation and growth of boehmite. Nitric acid, hydrochloric acid, and sulfuric acid are inorganic acidic regulators with mature processes and low cost, making them suitable for cost-sensitive lithium battery separator coating applications. Formic acid, acetic acid, oxalic acid, and citric acid are organic acidic regulators, possessing weaker acidity, good biodegradability, and the ability to reduce the introduction of impurity ions, making them particularly suitable for precision polishing applications with extremely stringent impurity requirements. In practical applications, a suitable acidic regulator can be selected based on specific needs and reaction conditions.

[0026] In some embodiments, the pH value of the acidic mixed slurry is 4 to 6.

[0027] In acidic environments with a pH of 4–6, industrial-grade aluminum hydroxide (Al(OH)3) dissolves more readily, forming soluble aluminate ions (such as [Al(OH)4)).- This step is a prerequisite for the formation of boehmite (γ-AlOOH), as aluminate ions are the basic building blocks for boehmite crystal growth. By adding boehmite seed crystals (D50 < 0.2 μm) to the acidic mixed slurry, under acidic conditions of pH 4–6, these boehmite seed crystals act as heterogeneous nucleation sites, inducing preferential epitaxial growth of boehmite on the seed crystal surface. This method effectively avoids the particle size inhomogeneity problem that may be caused by homogeneous nucleation of boehmite, resulting in more uniform boehmite particles. Finally, the acidic environment of pH 4–6 in the acidic mixed slurry has a significant impact on the growth direction of boehmite crystals. It inhibits anisotropic growth of boehmite crystals, preventing excessive growth in one direction that could lead to the formation of plate-like, rod-like, or irregular shapes. Conversely, the acidic conditions of pH 4–6 promote uniform growth of boehmite crystals in all directions, laying the foundation for the formation of spherical ultrafine boehmite structures. For example, the pH value of the acidic mixed slurry can be 4, 4.5, 5, 5.5, 6, etc.

[0028] In some embodiments, the D50 particle size of the boehmite seed crystal is <0.2 μm, and the mass of the boehmite seed crystal is 1% to 10% of the mass of the industrial-grade aluminum hydroxide.

[0029] The addition of boehmite seed crystals provides heterogeneous nucleation sites for boehmite nucleation, helping to avoid the particle size inhomogeneity problem caused by homogeneous boehmite nucleation. The D50 particle size is a statistical value, representing the particle size of 50% of the particles in a sample, and is an important indicator of particle size. In this embodiment, the D50 particle size of the boehmite seed crystals needs to be less than 0.2 μm. Such ultrafine seed crystals help induce uniform nucleation and growth of boehmite in the subsequent hydrothermal reaction, thereby forming near-spherical ultrafine boehmite with a concentrated particle size distribution. By adjusting the mass ratio of boehmite seed crystals, the growth rate and morphology of boehmite can be affected, thus achieving precise control over the particle size and morphology of the near-spherical ultrafine boehmite. Simultaneously, while ensuring the quality of the near-spherical ultrafine boehmite, reasonably controlling the amount of boehmite seed crystals used helps reduce production costs and improve the industrial application value of the method. In this embodiment, the mass of the boehmite seed crystals is 1% to 10% of the mass of industrial-grade aluminum hydroxide. This range ensures uniform nucleation and growth of boehmite while controlling production costs. For example, the D50 particle size of the boehmite seed crystals can be 0.1 μm, 0.12 μm, 0.14 μm, 0.16 μm, 0.18 μm, etc.; the mass of the boehmite seed crystals can be 1%, 3%, 5%, 7%, 9%, 10% of the mass of industrial-grade aluminum hydroxide, etc.

[0030] In some embodiments, the temperature of the first hydrothermal reaction is 190°C to 220°C, and the time of the first hydrothermal reaction is 2 hours to 8 hours.

[0031] In the first hydrothermal reaction, the acidic environment of the acidic mixed slurry not only promoted the dissolution of industrial-grade aluminum hydroxide but also provided heterogeneous nucleation sites through the addition of boehmite seed crystals. This induced preferential epitaxial growth of boehmite on the seed crystal surface, effectively avoiding the particle size inhomogeneity problem caused by homogeneous nucleation of boehmite. Simultaneously, the acidic conditions of the acidic mixed slurry inhibited the anisotropic growth of boehmite crystals, promoting uniform growth in all directions and laying the foundation for the formation of a spherical structure of ultrafine boehmite. Conducting the first hydrothermal reaction within the temperature range of 190℃ to 220℃ is beneficial for the dissolution of industrial-grade aluminum hydroxide and the formation of aluminate ions. Specifically, the high-temperature environment of 190℃ to 220℃ accelerated the chemical reaction rate, allowing industrial-grade aluminum hydroxide to be converted into aluminate ions more rapidly, which then formed boehmite crystals under the induction of the boehmite seed crystals. For example, the temperature of the first hydrothermal reaction can be 190℃, 195℃, 200℃, 205℃, 210℃, 215℃, 220℃, etc.

[0032] The reaction time is crucial for the growth and morphology control of boehmite crystals. Within a time range of 2 to 8 hours, boehmite crystals can undergo sufficient nucleation and growth under the induction of boehmite seed crystals. If the reaction time is less than 2 hours, the boehmite crystals may grow incompletely and have uneven particle size distribution; while if the reaction time is longer than 8 hours, it may cause excessive growth or agglomeration of boehmite crystals, which also affects the performance of near-spherical ultrafine boehmite. Therefore, selecting a reaction time of 2 to 8 hours is crucial for obtaining near-spherical ultrafine boehmite with uniform particle size and regular morphology. For example, the time for the first hydrothermal reaction can be 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, etc.

[0033] In some embodiments, the alkalinity regulator is at least one of sodium hydroxide, potassium hydroxide, and ammonia.

[0034] In the preparation of near-spherical ultrafine boehmite, an alkaline regulator is used to adjust the pH value of the first reaction slurry, thereby affecting the morphology and purity of the near-spherical ultrafine boehmite. The alkaline regulator can be at least one of sodium hydroxide, potassium hydroxide, or ammonia water. These alkaline substances can effectively raise the pH value of the first reaction slurry to the pH range of an alkaline mixed slurry, creating a strongly alkaline environment. This promotes the "aging" and "etching-recrystallization" modification of the boehmite precursor generated in the first hydrothermal reaction, thereby forming a regular near-spherical structure, removing some soluble impurities, and improving the purity of the near-spherical ultrafine boehmite.

[0035] In some embodiments, the pH value of the alkaline mixed slurry is 10 to 13.

[0036] In a strongly alkaline environment with a pH of 10–13, the small grains and sharp edges on the surface of the boehmite precursor are dissolved, reducing the surface energy of the particles and resulting in a smoother, more regular morphology. This process helps to form the ideal spherical structure of ultrafine boehmite. The alkaline conditions of the alkaline slurry also help to dissolve and remove some soluble impurities in the boehmite, such as Fe and Na metal ions, thereby purifying the spherical ultrafine boehmite. This is crucial for improving the chemical purity of spherical ultrafine boehmite, especially in applications with extremely high requirements for impurity content (such as high-end lithium battery separator coating and high-end precision polishing). The pH range of 10–13 for the alkaline slurry is a process window that ensures effective and easily controllable reaction, ensuring that the alkaline environment is strong enough to promote the ripening and etching-recrystallization processes while avoiding excessive dissolution of boehmite particles or other side reactions due to excessive alkalinity. For example, the pH value of the alkaline mixed slurry can be 10, 10.5, 11, 11.5, 12, 12.5, 13, etc.

[0037] In some embodiments, the temperature of the second hydrothermal reaction is 150°C to 180°C, and the time of the second hydrothermal reaction is 4h to 12h.

[0038] In the second hydrothermal reaction, the strongly alkaline environment of the alkaline mixed slurry and the reaction temperature of 150℃ to 180℃ jointly promote the "curing" and "etching-recrystallization" processes of the boehmite precursor. The alkaline conditions dissolve irregular small grains and sharp edges on the surface of the boehmite particles, reducing their surface energy and resulting in a smoother, more regular morphology, ultimately forming a spherical structure of near-spherical ultrafine boehmite. Within the temperature range of 150℃ to 180℃, the alkaline environment has the most significant modifying effect on the boehmite crystals, effectively improving the morphology and purity of the near-spherical ultrafine boehmite. If the second hydrothermal reaction temperature is below 150℃, incomplete modification of the boehmite particles may occur; if the second hydrothermal reaction temperature is above 180℃, it may cause agglomeration of the boehmite particles or changes in their crystal structure. For example, the temperature of the second hydrothermal reaction can be 150℃, 160℃, 170℃, 180℃, etc.

[0039] The duration of the second hydrothermal reaction directly affects the morphology modification and purification effect of boehmite. Controlling the second hydrothermal reaction time to 4-12 hours ensures sufficient modification of the boehmite particle morphology under alkaline conditions, as well as the complete dissolution and removal of soluble impurities in the boehmite. Experiments show that within the second hydrothermal reaction time range of 4-12 hours, the morphology and purity of near-spherical ultrafine boehmite reach their optimal state. If the second hydrothermal reaction time is shorter than 4 hours, the modification and purification of boehmite particles may be incomplete; if the second hydrothermal reaction time is longer than 12 hours, it will increase the production cost and energy consumption of near-spherical ultrafine boehmite, and the improvement in the performance of near-spherical ultrafine boehmite will no longer be significant. For example, the second hydrothermal reaction time can be 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, etc.

[0040] The temperature and time of the second hydrothermal reaction need to be controlled in a coordinated manner to achieve the best morphology modification and purification effect. Within the temperature range of 150℃ to 180℃ for the second hydrothermal reaction, and with a reaction time of 4h to 12h, spherical ultrafine boehmite with regular spherical morphology, ultrafine particle size and high purity can be prepared.

[0041] After the second hydrothermal reaction is completed, the second reaction slurry is subjected to solid-liquid separation and washing to obtain a boehmite wet filter cake. The boehmite wet filter cake is washed with deionized water or ethanol until the washing solution is neutral and the conductivity is stably below 50 μS / cm to ensure complete removal of Na. + Impurity ions were removed; subsequently, the washed boehmite wet filter cake was dried at a temperature below 350°C, and the dried boehmite blocks were subjected to airflow pulverization to obtain near-spherical ultrafine boehmite. In the embodiments of this application, "near-spherical" means that the projected outline of the boehmite particles under a scanning electron microscope image tends to be circular, but a certain degree of roughness, small irregular protrusions or depressions are allowed on the surface of the boehmite particles, and the boehmite particles as a whole do not exhibit obvious anisotropic structures (such as needle-like, plate-like, rod-like).

[0042] In some embodiments, the spheroidal ultrafine boehmite has a crystal structure of γ-AlOOH and possesses the following properties: Its microscopic morphology is spherical; The particle size distribution satisfies: D50 < 0.4 μm, D90 < 1.0 μm; Chemical purity >99.95wt%.

[0043] Through a two-step hydrothermal method (first hydrothermal reaction and second hydrothermal reaction), boehmite seed crystals are first used to induce boehmite nucleation and co-directional growth in an acidic environment, forming a prototype of near-spherical ultrafine boehmite. Subsequently, the boehmite precursor generated in the first hydrothermal reaction is ripened and modified by etching-recrystallization in an alkaline environment, resulting in smoother and more regular boehmite particle morphology, ultimately forming an ideal near-spherical structure. The near-spherical morphology helps form a dense and smooth coating, reduces clogging of diaphragm pores, lowers the viscosity of the coating slurry, and thus improves processing performance. In the field of precision polishing, near-spherical particles can effectively reduce scratches generated during polishing, achieving high-quality "nanoscale" planarization polishing.

[0044] The two-step hydrothermal method achieves precise control over the particle size of near-spherical ultrafine boehmite by accurately controlling reaction conditions (such as temperature, pH, and reaction time) and raw material ratios. The first hydrothermal reaction induces boehmite nucleation and directional growth, while the second hydrothermal reaction modifies and purifies the morphology of the boehmite precursor generated in the first hydrothermal reaction. The combined effect of these two hydrothermal steps results in small and uniformly distributed near-spherical ultrafine boehmite particles. The ultrafine particle size (D50 < 0.4 μm) and concentrated distribution (D90 < 1.0 μm) of the near-spherical ultrafine boehmite meet the stringent requirements for the particle size of coating materials in ultra-thin diaphragm coating, preventing near-spherical ultrafine boehmite particles from piercing the diaphragm, while simultaneously improving the uniformity and density of the boehmite coating. In the field of precision polishing, the ultrafine particle size of near-spherical ultrafine boehmite is fundamental to achieving ultra-smooth surface polishing effects on workpieces.

[0045] In the preparation of near-spherical ultrafine boehmite, by selecting high-purity industrial-grade aluminum hydroxide raw materials (industrial-grade aluminum hydroxide purity ≥98%), controlling hydrothermal reaction conditions, and subsequent washing and drying steps, the impurity content in the near-spherical ultrafine boehmite is effectively reduced. The second hydrothermal reaction also has a purification function, dissolving and removing some soluble impurities in the boehmite, such as Fe and Na metal ions. High-purity near-spherical ultrafine boehmite can avoid the influence of impurity ions on the electrochemical performance of lithium batteries, improving the safety and stability of lithium batteries. In the field of precision polishing, high-purity near-spherical ultrafine boehmite can prevent impurity ions from contaminating the workpiece surface, ensuring polishing quality. In the embodiments of this application, the specific impurity content control indicators for the near-spherical ultrafine boehmite are: Fe content <50ppm, Na content <200ppm, meeting the extremely high purity requirements for materials in high-end lithium battery separator coating and high-end precision polishing.

[0046] The present application is further illustrated below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national / industry standards; if there is no corresponding national / industry standard, they are performed according to general international standards, conventional conditions, or conditions recommended by the manufacturer.

[0047] Example 1 100g of industrial-grade aluminum hydroxide was mixed with 900g of deionized water to obtain a slurry. Nitric acid was added dropwise to the slurry until the pH reached 4.0. 5g of boehmite seed crystals (D50: 0.15μm) were added to the slurry, and stirring continued for 30 minutes. The slurry was transferred to a high-pressure reactor and reacted at 200℃ for 5 hours. After the reaction, the mixture was cooled to room temperature. Sodium hydroxide solution was slowly added to the slurry while stirring to adjust the pH to 10.5. The reactor was sealed again and reacted at 160℃ for 8 hours. After the reaction, the slurry was centrifuged and washed until the conductivity of the washings was <50μS / cm. It was then dried at 100℃ for 12 hours and pulverized by air jet milling to obtain near-spherical ultrafine boehmite powder.

[0048] Example 2 150g of industrial-grade aluminum hydroxide was mixed with 850g of deionized water to obtain a slurry. Hydrochloric acid was added dropwise with stirring until the slurry pH reached 5.0. 7.5g of boehmite seed crystals (D50: 0.15μm) were added to the slurry, and stirring continued for 30 minutes. The slurry was transferred to a high-pressure reactor and reacted at 200℃ for 6 hours. After the reaction, without cooling, ammonia water was directly introduced into the reactor to rapidly adjust the pH to 11.8. The reactor was sealed again and reacted at 150℃ for 6 hours. After the reaction, the slurry was centrifuged and washed until the conductivity of the washing solution was <50μS / cm. It was then dried at 100℃ for 12 hours and pulverized by air jet milling to obtain near-spherical ultrafine boehmite powder.

[0049] Example 3 100g of industrial-grade aluminum hydroxide was mixed with 900g of deionized water to obtain a slurry. Glacial acetic acid was added dropwise with stirring until the slurry pH reached 4.5. 5g of boehmite seed crystals (D50: 0.15μm) were added to the slurry, and stirring continued for 30 minutes. The slurry was transferred to a high-pressure reactor and reacted at 220℃ for 4 hours. After the reaction, the mixture was cooled to room temperature. Sodium hydroxide solution was slowly added to the slurry with stirring to adjust the pH to 10.5. The reactor was sealed again and reacted at 160℃ for 8 hours. After the reaction, the slurry was centrifuged and washed until the conductivity of the washings was <50μS / cm. It was then dried at 100℃ for 12 hours and pulverized by air jet milling to obtain near-spherical ultrafine boehmite powder.

[0050] Example 4 100g of industrial-grade aluminum hydroxide was mixed with 900g of deionized water to obtain a slurry. Citric acid was added dropwise with stirring until the slurry pH reached 6.0. 5g of boehmite seed crystals (D50: 0.15μm) were added to the slurry, and stirring continued for 30 minutes. The slurry was transferred to a high-pressure reactor and reacted at 205℃ for 4 hours. After the reaction, the mixture was cooled to room temperature. Sodium hydroxide solution was slowly added to the slurry with stirring to adjust the pH to 10.5. The reactor was sealed again and reacted at 160℃ for 8 hours. After the reaction, the slurry was centrifuged and washed until the conductivity of the washings was <50μS / cm. It was then dried at 100℃ for 12 hours and pulverized by air jet milling to obtain near-spherical ultrafine boehmite powder.

[0051] Comparative Example 1 100g of industrial-grade aluminum hydroxide was mixed with 900g of deionized water to obtain a slurry. 5g of boehmite seed crystals with a D50 of 0.15μm were added to the slurry, and stirring was continued for 30 minutes. The slurry was transferred to a high-pressure reactor and reacted at 200℃ for 5 hours. After the reaction, the slurry was centrifuged and washed until the conductivity of the washing liquid was <50μS / cm. It was then dried at 100℃ for 12 hours, and after air jet milling, spherical ultrafine boehmite powder was obtained.

[0052] The products obtained in Examples 1-4 and Comparative Example 1 were subjected to performance testing, and the results are shown in Table 1 below: Table 1

[0053] Results analysis: As shown in Table 1, the boehmite prepared by the method provided in this application has the characteristics of being ultrafine (D50<0.4 μm, D90<1.0 μm), spherical, and high-purity (>99.95%), making it particularly suitable as a coating material for ultra-thin separators of high-end lithium batteries and a high-end precision polishing material.

[0054] Furthermore, one or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages: Excellent product performance: The boehmite prepared in the embodiments of the present invention has high purity (>99.95%), ultra-fine particle size and regular spherical morphology, making it particularly suitable as a coating material for ultra-thin separators of high-end lithium batteries and a high-end precision polishing material.

[0055] Simple process and low cost: The embodiments of the present invention use inexpensive industrial aluminum hydroxide as raw material, the process is simple and easy to realize large-scale industrial production.

[0056] Appendix Figure 1-4 Detailed explanation: Figure 1The XRD pattern of the spheroidal ultrafine boehmite provided in Embodiment 1 of this application; by Figure 2 It can be seen that the obtained boehmite crystal form is γ-AlOOH.

[0057] Figure 2 This is a grain size diagram of the near-spherical ultrafine boehmite provided in Embodiment 1 of this application; by Figure 2 It can be seen that the obtained boehmite grain size distribution satisfies: D50=0.311μm, D90=0.586μm.

[0058] Figure 3 This is a SEM image of the spheroidal ultrafine boehmite provided in Embodiment 1 of this application; as shown... Figure 2 As shown, the obtained boehmite microstructure is quasi-spherical.

[0059] Figure 4 SEM image of the spheroidal ultrafine boehmite provided in Comparative Example 1 of this application; as shown Figure 2 As shown, the microstructure of the obtained boehmite is rhomboid in shape.

[0060] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed in this application.

Claims

1. A method for preparing a spheroid-like ultrafine boehmite, characterized by, The method comprises: mixing industrial-grade aluminum hydroxide with deionized water to obtain a slurry; adding an acid regulator to the slurry to adjust the pH value of the slurry to a set range, to obtain an acid mixed slurry; adding boehmite seeds to the acid mixed slurry to induce directional nucleation and growth of boehmite, to obtain a seed-containing acid mixed slurry; subjecting the seed-containing acid mixed slurry to a first hydrothermal reaction to achieve preliminary generation and morphology control of boehmite, to obtain a first reaction slurry; adding an alkaline regulator to the first reaction slurry to adjust the pH value of the first reaction slurry, to obtain an alkaline mixed slurry; subjecting the alkaline mixed slurry to a second hydrothermal reaction to achieve regularization of the morphology of boehmite and improvement of the purity, to obtain a second reaction slurry; subjecting the second reaction slurry to solid-liquid separation, washing, drying and crushing in sequence, to obtain a spherical-like ultrafine boehmite.

2. The method of claim 1, wherein, In the slurry, the mass fraction of aluminum hydroxide is 5%-20%.

3. The method of claim 1, wherein, The temperature of the first hydrothermal reaction is 190-220℃, and the time of the first hydrothermal reaction is 2-8h.

4. The method of claim 1, wherein, The temperature of the second hydrothermal reaction is 150-180℃, and the time of the second hydrothermal reaction is 4-12h.

5. The method of claim 1, wherein, The acid regulator is at least one of nitric acid, hydrochloric acid, sulfuric acid, formic acid, acetic acid, oxalic acid and citric acid.

6. The method of claim 1, wherein, The alkaline regulator is at least one of sodium hydroxide, potassium hydroxide and ammonia water.

7. The method of claim 1, wherein, The pH value of the acid mixed slurry is 4-6.

8. The method of claim 1, wherein, The pH value of the alkaline mixed slurry is 10-13.

9. The method of claim 1, wherein, The D50 particle size of the boehmite seeds is <0.2μm, and the mass of the boehmite seeds is 1%-10% of the mass of the industrial-grade aluminum hydroxide.

10. The method of claim 1, wherein, The crystal structure of the spherical-like ultrafine boehmite is γ-AlOOH, and the spherical-like ultrafine boehmite has the following properties: The micro-morphology is spherical-like; The particle size distribution satisfies D50<0.4μm and D90<1.0μm; The chemical purity is >99.95wt%.

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