A method for preparing nano-boehmite and its application in lithium-ion battery separators.

Abstract

This invention discloses a method for preparing nano-boehmite and its application in lithium-ion battery separators, belonging to the field of inorganic nanomaterial preparation technology. The method includes five steps: raw material calcination and activation, preparation of precursor slurry, hydrothermal synthesis reaction, washing and filtration, and drying and depolymerization. Calcination is carried out in a dynamic calcination furnace, whose exhaust mechanism can promptly remove water vapor. During discharge, the switching mechanism automatically opens the discharge cover, achieving continuous production with no material sticking to the wall and no residue. The obtained nano-boehmite is characterized by low sodium content, uniform particle size, and good dispersibility. This material can be formulated with binders and other agents to form a ceramic coating slurry. After coating and drying, a robust nano-ceramic coating is formed on the surface of a polyolefin-based membrane. This coating significantly improves the thermal stability, electrolyte wettability, and puncture resistance of the separator, thereby improving the battery's safety performance and cycle life.

Description

Technical Field

[0001] This invention relates to the field of inorganic nanomaterial preparation technology, and in particular to a method for preparing nano-boehmite and its application in lithium-ion battery separators. Background Technology

[0002] Nanoboehmite (γ-AlOOH), as a crystalline aluminum hydroxide nanomaterial, possesses a unique layered structure and abundant surface hydroxyl groups, exhibiting a high specific surface area (typically reaching 150–350 m²). 2 It possesses good thermal stability (thermal decomposition temperature above approximately 500℃) and excellent chemical and mechanical stability. These properties have led to its mature applications in traditional industrial fields such as catalyst supports, inorganic flame retardants, precision ceramics, coating reinforcement, and polymer composites. In recent years, with the rapid development of the new energy industry, especially lithium-ion battery technology, nano-boehmite has been widely studied and gradually industrialized for use in functional coatings of lithium-ion battery separators due to its high insulation, resistance to electrolyte corrosion, and good compatibility with polyolefin substrates.

[0003] In lithium-ion batteries, the separator, as a key inner component, needs to possess good ion permeability, electronic insulation, appropriate pore structure, and sufficient thermomechanical strength. Currently, commercially available separators are mainly made of polyethylene (PE), polypropylene (PP), or their multilayer composites. While these meet basic performance requirements, their melting points are relatively low (PE approximately 130–135℃, PP approximately 160–165℃). Under abnormal battery temperature rise or localized overheating, they are prone to shrinkage and melting, leading to direct contact between the positive and negative electrodes and causing a short circuit. In severe cases, this can trigger thermal runaway or even combustion and explosion. To improve the high-temperature stability of the separator, the industry commonly uses a ceramic coating method. Among these, nano-boehmite, due to its high heat resistance, high purity, low density, and good coating uniformity, has become one of the most promising ceramic coating materials. Boehmite coatings can effectively increase the thermal pore-closing temperature of the separator, delay thermal shrinkage, enhance electrolyte wettability and liquid absorption and retention capacity, and also improve the mechanical puncture resistance of the separator, thereby improving the overall safety and cycle life of the battery. It is worth noting that for nano-boehmite used in lithium-ion battery separator coatings, a higher specific surface area is not necessarily better. Excessively high specific surface area can lead to increased slurry viscosity, difficulty in coating, and potentially additional side reaction risks during battery cycling. Therefore, obtaining nano-boehmite with uniform particle size and regular morphology but a moderate specific surface area (e.g., ≤35 m² / g) through process control is more conducive to forming a dense ceramic coating with high mechanical strength and good compatibility with the electrolyte.

[0004] However, the properties of nano-boehmite are highly dependent on its physicochemical characteristics, such as crystal morphology, particle size distribution, specific surface area, and impurity content. While existing hydrothermal methods can prepare nano-boehmite, the following problems remain for industrial application: water vapor is difficult to remove in time during the calcination stage, easily leading to powder agglomeration; dispersants may introduce impurity ions; and hard agglomeration easily occurs during the drying process. Furthermore, existing calcination equipment has a low degree of automation, making it difficult to achieve efficient degassing and smooth material discharge simultaneously.

[0005] Besides the inherent problems with the material synthesis process itself, existing production equipment also suffers from significant deficiencies in functional integration and automated control. Particularly in the dynamic calcination section, traditional calcining furnaces often struggle to simultaneously meet the process requirements of "continuous and efficient venting" and "smooth and rapid material discharge." Most equipment lacks an automatic venting-sealing mechanism that switches between calcination and discharge states, requiring manual intervention for pipe connections and disconnections. This is not only cumbersome and inefficient but also prone to material contamination, batch-to-batch cross-contamination, and decreased product consistency due to steam condensation and backflow or delayed discharge. Furthermore, existing furnace bodies often lack automatic tilting functionality during discharge, or the venting ports cannot disengage synchronously when tilted, affecting the integrity of the discharge and the smoothness of equipment operation.

[0006] Therefore, developing a nano-boehmite preparation technology with high process integration, scalable production, stable product quality, and high degree of equipment automation is of clear industrial necessity and technological urgency. An ideal preparation system should be able to optimize the entire process from raw material calcination, hydrothermal synthesis, washing and purification to drying and depolymerization. In particular, it needs to integrate intelligent venting and discharging devices in the precursor activation stage to solve the common problems of water vapor residue and poor discharging. Based on this, further developing a boehmite slurry formulation and coating process suitable for lithium-ion battery separator coatings will strongly promote the commercialization of high-safety, high-power, and long-life lithium-ion batteries, possessing significant scientific and technological value and broad market application prospects. Summary of the Invention

[0007] The purpose of this invention is to provide a continuous preparation method for nano-boehmite with low sodium content and good dispersibility, as well as a dynamic calcination furnace that enables efficient exhaust and automated material discharge during the calcination process, and to apply the obtained nano-boehmite to high-performance lithium-ion battery separators. By precisely controlling the calcination temperature within a specific window of 500±10℃, the aim is to achieve a full conversion of aluminum hydroxide to active alumina while avoiding over-sintering, thus providing an ideal precursor for subsequent hydrothermal synthesis of boehmite.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing nano-boehmite, the specific steps of which are as follows:

[0009] S1. Raw material calcination activation: Aluminum hydroxide raw material is calcined at 500±10℃ for 1±0.2 hours to obtain activated alumina powder;

[0010] S2. Preparation of precursor slurry: The alumina powder and pure water are mixed at a solid-liquid ratio of 1:9, a dispersant is added, and the mixture is stirred evenly to form a precursor slurry;

[0011] S3. Hydrothermal synthesis: The precursor slurry is placed in a reactor and hydrothermal reaction is carried out by programmed temperature increase. First, the temperature is increased to 120±5℃ and held for 12±1 hours, then the temperature is increased to 180±5℃ and held for another 12±1 hours to obtain nano-boehmite slurry.

[0012] S4. Washing and filtration: Wash the nano-boehmite slurry with pure water and filter it until the pH of the filtrate is ≤8 to obtain nano-boehmite filter cake;

[0013] S5. Drying and depolymerization: After drying the nano-boehmite filter cake, it is subjected to air-jet milling and depolymerization to obtain nano-boehmite powder.

[0014] As a further aspect of the present invention: in step S2, the conductivity of the pure water is <1.1 μS / cm; the dispersant includes sodium polyacrylate and polyethylene glycol, and their addition amounts are 6‰ and 8‰ of the mass of alumina powder, respectively.

[0015] As a further aspect of the present invention: in step S3, the rate of temperature increase is controlled at 1-1.5℃ / minute.

[0016] As a further embodiment of the present invention: in step S5, the drying temperature is 200±10℃; the particle size D50 of the nano-boehmite powder is 100±20 nanometers, the sodium content is <300 ppm, and the specific surface area is ≤35 m² / g.

[0017] As a further aspect of the present invention: in step S1, the calcination is carried out in a dynamic calcination furnace, and the water vapor generated during the calcination process is discharged in real time through an exhaust mechanism; the exhaust mechanism can automatically separate from the furnace body when the material is discharged from the dynamic calcination furnace.

[0018] As a further embodiment of the present invention: the calcination process in step S1 is carried out in a dynamic calcination furnace, which includes a base, a rotating plate rotatably connected to the top of the base, an organic body fixedly connected to the top of the rotating plate, a kiln body being provided in the inner cavity of the organic body, a rotating cover and a discharge cover being respectively provided at the two ends of the kiln body, the rotating cover being rotatably connected to the kiln body, a toothed ring being fixedly connected to the outer wall of the kiln body near the rotating cover, a limiting ring being fixedly connected to the outer wall of the kiln body near the discharge cover, a support base being fixedly connected to the top of the rotating plate, and the limiting ring being rotatably connected to the kiln body. The inner wall of the support base is connected to the outer wall of the kiln body, and a feed inlet is provided on one side of the gear ring. The top of the feed inlet is fixedly connected to a cover plate by bolts. The top of the rotating plate is symmetrically fixedly connected to a mounting base below the gear ring. The top of the mounting base is rotatably connected to a first spur gear. The outer wall of the gear ring has a first tooth groove, which meshes with the first spur gear. A motor is installed on the outer wall of one of the mounting bases. The first spur gear is connected to the output end of the motor. The steam in the kiln body is discharged through an exhaust mechanism. The discharge cover is automatically moved by a switching mechanism.

[0019] As a further embodiment of the present invention: the exhaust mechanism includes a mounting frame, which is fixedly connected to the top of the base and located above the rotating plate. An air inlet pipe and an exhaust pipe are fixedly connected to the outer wall of the mounting frame. A connecting cylinder is slidably sleeved at the bottom end of both the air inlet pipe and the exhaust pipe. A connecting hole is opened on the outer wall of both the rotating cover and the discharge cover. A displacement frame is fixedly connected to the top end of the connecting cylinder. A second spur gear is rotatably connected to the inner wall of the mounting frame. The two displacement frames are respectively in contact with the top and bottom ends of the second spur gear. A hydraulic cylinder is installed inside the base. A displacement plate is connected to the output end of the hydraulic cylinder. A displacement groove for the displacement plate to slide is opened inside the base. A vertical plate extending to the bottom end of the rotating plate is slidably connected inside the base. A connecting plate is fixedly connected to the outer wall of the vertical plate and is located above the displacement plate. A pushing block extending into the inner cavity of the displacement groove is slidably connected inside the base. A spring is connected between the pushing block and the base. A pushing frame is fixedly connected to the top end of the pushing block. The pushing frame is fixedly connected to one of the connecting cylinders.

[0020] As a further embodiment of the present invention: the switching mechanism includes a rotating groove, the rotating groove being formed at the top of the base, the rotating plate being located on the inner wall of the rotating groove, a fixing rod being fixedly connected to the inner wall of the rotating groove, the fixing rod passing through the rotating plate, a first bevel gear being symmetrically fixedly connected to the outer wall of the fixing rod, a gear plate being rotatably connected to the inner wall of the rotating plate on the outer wall of the first bevel gear, a second bevel gear being rotatably connected to the inner wall of the rotating plate on the outer wall of the gear plate, a connecting shaft being fixedly connected to the top of the second bevel gear, a third spur gear being fixedly connected to the top of the connecting shaft, and a toothed rod being slidably connected to the inner wall of the support base on the outer wall of the third spur gear, the toothed rod being fixedly connected to the discharge cover.

[0021] As a further embodiment of the present invention: the push block extends to the bottom end of the displacement groove cavity and is provided with an inclined surface, and the outer wall of the connecting cylinder is in contact with the inner wall of the connecting hole.

[0022] As a further embodiment of the present invention: the outer wall of the displacement frame is provided with a second toothed groove, the second toothed groove meshing with the second spur gear, and a guide frame is fixedly connected to the inner wall of the mounting frame, the inner wall of the guide frame being in contact with the outer wall of the displacement frame.

[0023] As a further embodiment of the present invention: one end of the gear disk is provided with a first gear tooth, which meshes with the first bevel gear.

[0024] As a further embodiment of the present invention: a second gear tooth is provided at the other end of the gear disk, and the second gear tooth meshes with the second bevel gear.

[0025] As a further embodiment of the present invention: the outer wall of the gear is provided with a third tooth groove, which meshes with the third spur gear.

[0026] A method for preparing nano-boehmite and applying it to a lithium-ion battery separator includes the following steps: mixing the nano-boehmite powder, binder and solvent to prepare a ceramic coating slurry; uniformly coating the ceramic coating slurry onto the surface of a polyolefin base film; and forming a nano-boehmite ceramic coating on the base film surface after drying and curing.

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] 1. The preparation method of nano-boehmite of the present invention achieves high purity and low agglomeration of nano-boehmite product simultaneously through systematic parameter control of precursor treatment, hydrothermal synthesis, and post-treatment processes. This method activates the raw materials at a specific calcination temperature and regulates crystal growth using a two-stage hydrothermal program, combined with precise washing endpoint control, ensuring that the sodium content of the product is consistently below 300 ppm and the particle size is uniform. Finally, through matched drying and deagglomeration processes, the hard agglomeration of nanoparticles is effectively suppressed, resulting in well-dispersible nanoparticles suitable for high-performance ceramic coatings.

[0029] 2. The preparation method of nano-boehmite of the present invention controls parameters in a coordinated manner from solid-liquid ratio, dispersant ratio, hydrothermal temperature and time, to pH value at the washing endpoint and drying temperature. This transforms the synthesis of nano-boehmite into a standardized process that can be precisely controlled, thereby ensuring a high degree of consistency and reliability of the physicochemical properties of the product in large-scale production.

[0030] 3. The dynamic calcining furnace and integrated exhaust and switching mechanism described in this invention solve a key bottleneck in the precursor activation process from an engineering perspective. Its continuous dynamic tumbling and efficient exhaust design ensures uniform heating of the material during calcination and timely removal of water vapor from the reaction zone. This fundamentally inhibits powder pre-agglomeration and impurity (such as Na⁺) residue caused by localized over-humidification or steam condensation, providing a highly active, low-caking alumina precursor for subsequent hydrothermal synthesis, directly contributing to the low sodium content and good dispersibility of the final product (nano-boehmite). Simultaneously, the automatic disengagement of the exhaust mechanism and the synchronous tilting and opening of the kiln body during the discharge stage achieve a fully enclosed and automated connection between the calcination-cooling-discharge sections. This not only eliminates contamination introduced by manual operation and cross-contamination between batches but also avoids material retention and performance fluctuations caused by poor discharge, thus ensuring the process stability and repeatability from raw materials to intermediate products. It is a crucial equipment cornerstone for continuous and standardized production.

[0031] 4. The equipment of this invention employs an automated mechanism linking the exhaust mechanism and the switching mechanism, achieving intelligent coupling and precise timing control of chemical unit operations (calcination, exhaust, and discharge). The exhaust mechanism maintains a sealed connection during calcination and automatically decouples via hydraulic drive after the discharge command is issued; simultaneously, the mechanical transmission switching mechanism triggered by the kiln tilt opens the discharge cover synchronously. This "one-button" operation replaces the cumbersome steps of manually connecting / disconnecting pipes and manually opening covers required by traditional intermittent furnaces, significantly shortening batch cycles and improving equipment utilization. More importantly, it eliminates process parameter drift caused by human delays or errors (such as inconsistent material cooling times after calcination or exposure to contamination), ensuring that key process parameters can be accurately reproduced in each cycle. This high degree of operational certainty and timing controllability is the fundamental guarantee for ensuring parameter coordination and consistent results throughout the entire nano-boehmite synthesis process (from precursor preparation to post-processing), significantly improving the robustness of the entire production system and product qualification rate. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the structure of the dynamic calcining furnace described in this invention;

[0033] Figure 2 This is a schematic diagram of the internal structure of the kiln body of the dynamic calcining furnace described in this invention;

[0034] Figure 3 This is a schematic diagram of the installation of the first spur gear in the dynamic calcining furnace described in this invention;

[0035] Figure 4 This is a schematic diagram of the internal structure of the mounting frame of the dynamic calcining furnace described in this invention;

[0036] Figure 5 The dynamic calcining furnace described in this invention Figure 4 Enlarged view of point A in the middle;

[0037] Figure 6 This is a schematic diagram of the installation of the fixing rod of the dynamic calcining furnace described in this invention;

[0038] Figure 7 This is a schematic diagram of the installation of the first bevel gear in the dynamic calcining furnace described in this invention;

[0039] Figure 8 This is a schematic diagram of the installation of the toothed rod of the dynamic calcining furnace described in this invention.

[0040] In the diagram: 1. Base; 2. Rotating plate; 3. Machine body; 4. Kiln body; 5. Rotating cover; 6. Discharge cover; 7. Feed inlet; 8. Exhaust mechanism; 801. Mounting frame; 802. Air inlet pipe; 803. Exhaust pipe; 804. Connecting cylinder; 805. Connecting hole; 806. Displacement frame; 807. Second spur gear; 808. Hydraulic cylinder; 809. Displacement plate; 810. Displacement groove; 811. Connecting plate; 812. Vertical plate; 813. 814. Push block; 815. Spring; 816. Push frame; 9. Switching mechanism; 901. Rotating groove; 902. Fixed rod; 903. First bevel gear; 904. Gear disc; 905. Second bevel gear; 906. Connecting shaft; 907. Third spur gear; 908. Gear rack; 10. Cover plate; 11. Limiting ring; 12. Support base; 13. Gear ring; 14. Mounting base; 15. First spur gear; 16. Motor; 17. Guide frame. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. In the description of this invention, it should be noted that unless otherwise explicitly specified and limited, the terms "installed," "connected," "linked," and "set up" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances. The following describes embodiments of the invention based on its overall structure.

[0043] Unless otherwise specified, the raw materials and equipment involved in the following embodiments and comparative examples are as follows:

[0044] Aluminum hydroxide raw material: D50≈1μm, industrial grade. Pure water: conductivity <1.1μS / cm. Dynamic calcination furnace: structure as per the instruction manual. Figure 1-8 As shown in the corresponding description. Airflow mill: a commonly used ultrafine grinding equipment on the market. Example 1

[0045] Please see Figures 1 to 8 In this embodiment of the invention, a method for preparing nano-boehmite includes the following specific steps:

[0046] S1. Raw material calcination and activation: Aluminum hydroxide raw material is fed into the kiln body 4 of the dynamic calcination furnace. The motor 16 is started to make the kiln body 4 rotate slowly and heat it to 500℃ for calcination for 1 hour. During the calcination process, the exhaust mechanism 8 is started, and the fan continuously discharges the water vapor generated by the reaction through the exhaust pipe 803.

[0047] S2. Preparation of precursor slurry: The alumina powder obtained in step S1 is mixed with pure water at a solid-liquid ratio of 1:9. Sodium polyacrylate (6‰ by weight of alumina powder) and polyethylene glycol (8‰ by weight) are added as dispersants. The mixture is stirred in a mixer at 20 rpm for 1 hour to form a homogeneous precursor slurry.

[0048] S3. Hydrothermal Synthesis Reaction: The precursor slurry is pumped into a high-pressure reactor. The temperature is first increased to 120°C at a rate of 1.0°C / min and held for 12 hours; then, the temperature is increased to 180°C at the same rate and held for another 12 hours. The reaction is then allowed to cool naturally after completion.

[0049] S4. Washing and Filtration: The cooled nano-boehmite slurry is washed multiple times with pure water and then filtered using a plate and frame filter press until the pH of the filtrate stabilizes at 7.5.

[0050] S5. Drying and Depolymerization: The obtained nano-boehmite filter cake was placed in an oven at 200℃ and dried for 6 hours. The dried lumpy material was then fed into an air jet mill for depolymerization to obtain the finished nano-boehmite powder.

[0051] Please refer to this carefully. Figures 1 to 8 The calcination process in step S1 is carried out in a dynamic calcination furnace, which includes a base 1, a rotating plate 2 rotatably connected to the top of the base 1, an organic body 3 fixedly connected to the top of the rotating plate 2, a kiln body 4 provided in the inner cavity of the organic body 3, and an electric heating device capable of heating the kiln body 4 installed inside the organic body 3.

[0052] A rotating cover 5 and a discharge cover 6 are respectively provided at the two ends of the kiln body 4. The rotating cover 5 is rotatably connected to the kiln body 4. A toothed ring 13 is fixedly connected to the outer wall of the kiln body 4 near the rotating cover 5. A limiting ring 11 is fixedly connected to the outer wall of the kiln body 4 near the discharge cover 6. A support base 12 is fixedly connected to the top of the rotating plate 2. The limiting ring 11 is rotatably connected to the inner wall of the support base 12. A feed inlet 7 is provided on the outer wall of the kiln body 4 on the side of the toothed ring 13. A cover plate 10 is fixedly connected to the top of the feed inlet 7 by bolts. A mounting base 14 is symmetrically fixedly connected to the top of the rotating plate 2 below the toothed ring 13. A first spur gear 15 is rotatably connected to the top of the mounting base 14. A first tooth groove is opened on the outer wall of the toothed ring 13. The first tooth groove meshes with the first spur gear 15. A motor 16 is installed on the outer wall of one mounting base 14. The first spur gear 15 is connected to the output end of the motor 16. The steam in the kiln body 4 is discharged through the exhaust mechanism 8. The discharge cover 6 is automatically moved by the switching mechanism 9.

[0053] In this embodiment: when the feed inlet 7 is facing upwards, the cover plate 10 is removed by bolts to open the feed inlet 7, and high-quality aluminum hydroxide is fed into the kiln body 4 through the feed inlet 7. Then, the feed inlet 7 is closed, and the motor 16 is started. The motor 16 drives the first spur gear 15 to rotate, which in turn drives the gear ring 13 to rotate, which in turn drives the kiln body 4 to rotate. At this time, the limiting ring 11 rotates within the support base 12. While the kiln body 4 rotates, the discharge cover 6 and the rotating cover 5 remain stationary. The rotation of the kiln body 4 ensures uniform calcination of the internal material, preventing agglomeration. It is worth noting that an electromagnetic coil or electric heating coil is installed inside the machine body 3 to heat the kiln body 4 using electromagnetic induction heating or electric heating.

[0054] Please refer to this carefully. Figures 2 to 5The exhaust mechanism 8 includes a mounting bracket 801, which is fixedly connected to the top of the base 1 and located above the rotating plate 2. An air inlet pipe 802 and an exhaust pipe 803 are fixedly connected to the outer wall of the mounting bracket 801. A connecting cylinder 804 is slidably sleeved at the bottom end of both the air inlet pipe 802 and the exhaust pipe 803. Connecting holes 805 are provided on the outer walls of the rotating cover 5 and the discharge cover 6. A displacement bracket 806 is fixedly connected to the top of the connecting cylinder 804. A second spur gear 807 is rotatably connected to the inner wall of the mounting bracket 801. The two displacement brackets 806 contact the top and bottom ends of the second spur gear 807, respectively. A hydraulic cylinder is installed inside the base 1. 808, the output end of the hydraulic cylinder 808 is connected to a displacement plate 809, the base 1 has a displacement groove 810 for the displacement plate 809 to slide, the base 1 has a vertical plate 812 extending to the bottom of the rotating plate 2 slidably connected, the outer wall of the vertical plate 812 is fixedly connected to a connecting plate 811, the connecting plate 811 is located above the displacement plate 809, the base 1 has a pushing block 813 extending to the inner cavity of the displacement groove 810 slidably connected, the pushing block 813 is connected to the base 1 with a spring 814, the top of the pushing block 813 is fixedly connected to a pushing frame 815, the pushing frame 815 is fixedly connected to a connecting cylinder 804.

[0055] In this embodiment: During calcination, the connecting cylinder 804 is located on the inner wall of the connecting hole 805, and the generated water vapor is discharged through the exhaust pipe 803; when discharging, the hydraulic cylinder 808 is activated, and the hydraulic cylinder 808 drives the displacement plate 809 to move upward. The displacement plate 809 first contacts the pushing block 813, pushing the pushing block 813 to move, which compresses the spring 814. The displacement of the pushing block 813 drives the pushing frame 815 to move, and the displacement of the pushing frame 815 drives the connecting cylinder 804 to move. The displacement of the connecting cylinder 804 drives the displacement frame 806 to move, and the displacement of the displacement frame 806 drives the second spur gear 807 to rotate. The rotation of the second spur gear 807 drives the other displacement frame 806 to move, so that the two connecting cylinders 804 move synchronously in opposite directions. The connecting cylinder 804 moves out of the connecting hole 805, so that the air inlet pipe 802 and the exhaust pipe 803 are separated from the kiln body 4, avoiding affecting the subsequent movement of the kiln body 4.

[0056] Then, the displacement plate 809 continues to move and comes into contact with the connecting plate 811, pushing the connecting plate 811 to move. The displacement of the connecting plate 811 causes the vertical plate 812 to move, and the vertical plate 812 moves upward, pushing the rotating plate 2 to rotate. The rotation of the rotating plate 2 causes the kiln body 4 to rotate and tilt. At this time, the kiln body 4 continues to tilt and rotate, and the material inside the kiln body 4 slides along the kiln body 4 and is discharged from the opening where the discharge cover 6 is installed (at this time, the switching mechanism 9 has driven the discharge cover 6 to move, so that the opening is open). After the discharge is completed, the displacement plate 809 moves downward, causing the rotating plate 811 to move downward. The rotation is horizontal, causing the kiln body 4 to also be horizontal. Then, the push block 813 is reset by the spring force of the spring 814. The displacement of the push block 813 causes the push frame 815 and the connecting cylinder 804 to move. The connecting cylinder 804 is inserted into the connecting hole 805, connecting both the air inlet pipe 802 and the exhaust pipe 803 to the kiln body 4, facilitating the discharge of water vapor through these pipes. Simultaneously, when the kiln body 4 is tilted, the air inlet pipe 802 and the exhaust pipe 803 are automatically separated from the kiln body 4, preventing obstruction of its movement. It is worth noting that a fan is installed on the outer wall of the exhaust pipe 803 to drive water vapor through it for discharge. A spherical filter screen is installed at the end of the connecting cylinder 804 inserted into the connecting hole 805 to prevent the fan from accidentally drawing material into the kiln.

[0057] Please refer to this carefully. Figures 6 to 8 The switching mechanism 9 includes a rotating groove 901, which is located at the top of the base 1. A rotating plate 2 is located on the inner wall of the rotating groove 901. A fixing rod 902 is fixedly connected to the inner wall of the rotating groove 901. The fixing rod 902 passes through the rotating plate 2. A first bevel gear 903 is symmetrically fixedly connected to the outer wall of the fixing rod 902. A gear disk 904 is rotatably connected to the inner wall of the rotating plate 2 on the outer wall of the first bevel gear 903. A second bevel gear 905 is rotatably connected to the inner wall of the rotating plate 2 on the outer wall of the gear disk 904. A connecting shaft 906 is fixedly connected to the top of the second bevel gear 905. A third spur gear 907 is fixedly connected to the top of the connecting shaft 906. A gear rod 908 is slidably connected to the inner wall of the support base 12 on the outer wall of the third spur gear 907. The gear rod 908 is fixedly connected to the discharge cover 6.

[0058] In this embodiment: when the rotating plate 2 rotates, the rotating plate 2 rotates around the fixed rod 902 as the axis. The rotating plate 2 rotates relative to the fixed rod 902. At the same time, the gear disk 904 rotates around the first bevel gear 903. The gear disk 904 is driven to rotate by the first bevel gear 903, which in turn drives the second bevel gear 905 to rotate. The rotation of the second bevel gear 905 drives the connecting shaft 906 to rotate. The rotation of the connecting shaft 906 drives the third spur gear 907 to rotate. The rotation of the third spur gear 907 drives the rack 908 to move. The movement of the rack 908 drives the discharge cover 6 to move away from the kiln body 4, opening one end of the kiln body 4, thereby facilitating the discharge of materials. This design facilitates the automatic opening of one end of the kiln body 4 when the kiln body 4 is rotated in an inclined position, thus facilitating the discharge of materials.

[0059] Please refer to this carefully. Figures 2 to 5 The push block 813 extends to the bottom of the cavity of the displacement groove 810 and is provided with an inclined surface. The outer wall of the connecting cylinder 804 fits against the inner wall of the connecting hole 805.

[0060] In this embodiment: the hydraulic cylinder 808 operates to drive the displacement plate 809 to move upward. The displacement plate 809 first contacts the push block 813, pushing the push block 813 to move, causing compression on the spring 814. The displacement of the push block 813 drives the push frame 815 to move, and the displacement of the push frame 815 drives the connecting cylinder 804 to move, so that the connecting cylinder 804 moves out of the connecting hole 805.

[0061] Please refer to this carefully. Figures 2 to 5 The outer wall of the displacement frame 806 is provided with a second toothed groove, which meshes with the second spur gear 807. The inner wall of the mounting frame 801 is fixedly connected with a guide frame 17, and the inner wall of the guide frame 17 is in contact with the outer wall of the displacement frame 806.

[0062] In this embodiment: the displacement of the push frame 815 causes the connecting cylinder 804 to move, the displacement of the connecting cylinder 804 causes the displacement frame 806 to move, the displacement of the displacement frame 806 causes the second spur gear 807 to rotate, and the rotation of the second spur gear 807 causes another displacement frame 806 to move, so that the two connecting cylinders 804 move synchronously in opposite directions. The connecting cylinder 804 moves out of the connecting hole 805, so that the air inlet pipe 802 and the exhaust pipe 803 are separated from the kiln body 4.

[0063] Please refer to this carefully. Figures 6 to 8 One end of the gear disk 904 is provided with a first gear tooth, which meshes with the first bevel gear 903. The other end of the gear disk 904 is provided with a second gear tooth, which meshes with the second bevel gear 905.

[0064] In this embodiment: when the rotating plate 2 rotates, the rotating plate 2 rotates around the fixed rod 902 as the axis. The rotating plate 2 rotates relative to the fixed rod 902. At the same time, the gear disk 904 rotates around the first bevel gear 903. The gear disk 904 is pushed by the first bevel gear 903 to rotate, which in turn drives the second bevel gear 905 to rotate. The rotation of the second bevel gear 905 drives the connecting shaft 906 to rotate.

[0065] Please refer to this carefully. Figures 6 to 8 The outer wall of the rack 908 is provided with a third tooth groove, which meshes with the third spur gear 907.

[0066] In this embodiment: the rotation of the connecting shaft 906 drives the third spur gear 907 to rotate, the rotation of the third spur gear 907 drives the rack 908 to move, and the movement of the rack 908 drives the discharge cover 6 to move. Example 2

[0067] S1. Raw material calcination and activation: Aluminum hydroxide raw material is fed into the kiln body 4 of the dynamic calcination furnace. The motor 16 is started to make the kiln body 4 rotate slowly and heat it to 510℃ for calcination for 1.2 hours. During the calcination process, the exhaust mechanism 8 is started, and the fan continuously discharges the water vapor generated by the reaction through the exhaust pipe 803.

[0068] S2. Preparation of precursor slurry: The alumina powder obtained in step S1 is mixed with pure water at a solid-liquid ratio of 1:9. Sodium polyacrylate (6‰ by weight of alumina powder) and polyethylene glycol (8‰ by weight) are added as dispersants. The mixture is stirred in a mixer at 20 rpm for 1 hour to form a homogeneous precursor slurry.

[0069] S3. Hydrothermal Synthesis Reaction: The precursor slurry is pumped into a high-pressure reactor. First, the temperature is increased to 120°C at a rate of 1.5°C / min and held for 12 hours; then, the temperature is increased to 185°C at the same rate and held for another 12 hours. After the reaction is complete, the mixture is allowed to cool naturally.

[0070] S4. Washing and Filtration: The cooled nano-boehmite slurry is washed multiple times with pure water and then filtered using a plate and frame filter press until the pH of the filtrate stabilizes at 7.5.

[0071] S5. Drying and Depolymerization: The obtained nano-boehmite filter cake was placed in an oven at 200℃ and dried for 6 hours. The dried lumpy material was then fed into an air jet mill for depolymerization to obtain the finished nano-boehmite powder. Example 3

[0072] S1. Raw material calcination and activation: Aluminum hydroxide raw material is fed into the kiln body 4 of the dynamic calcination furnace. The motor 16 is started to slowly rotate the kiln body 4 and heat it to 490℃ for calcination for 0.8 hours. During the calcination process, the exhaust mechanism 8 is started, and the fan continuously discharges the water vapor generated by the reaction through the exhaust pipe 803.

[0073] S2. Preparation of precursor slurry: The alumina powder obtained in step S1 is mixed with pure water at a solid-liquid ratio of 1:9. Sodium polyacrylate (6‰ by weight of alumina powder) and polyethylene glycol (8‰ by weight) are added as dispersants. The mixture is stirred in a mixer at 20 rpm for 1 hour to form a homogeneous precursor slurry.

[0074] S3. Hydrothermal Synthesis Reaction: The precursor slurry is pumped into a high-pressure reactor. First, the temperature is increased to 120°C at a rate of 1.0°C / min and held for 12 hours; then, the temperature is increased to 175°C at the same rate and held for another 12 hours. After the reaction is complete, the mixture is allowed to cool naturally.

[0075] S4. Washing and Filtration: The cooled nano-boehmite slurry is washed multiple times with pure water and then filtered using a plate and frame filter press until the pH of the filtrate stabilizes at 7.5.

[0076] S5. Drying and Depolymerization: The obtained nano-boehmite filter cake was placed in an oven at 200℃ and dried for 6 hours. The dried lumpy material was then fed into an air jet mill for depolymerization to obtain the finished nano-boehmite powder.

[0077] Comparative Example 1 uses traditional static calcination without continuous exhaust.

[0078] The only difference between this comparative example and Example 1 is step S1: calcination was performed using a static box-type muffle furnace under the same conditions of 500°C for 1 hour. During calcination, the furnace door was kept closed, preventing the generated water vapor from escaping in time, which condensed on the inner wall of the furnace. After calcination, slight agglomeration and dampness were observed in the alumina powder. Subsequent steps S2 to S5 were exactly the same as in Example 1.

[0079] Comparative Example 2: Simplified Hydrothermal

[0080] The only difference between this comparative example and Example 1 is step S3: the two-stage heating and holding process is omitted. The precursor slurry is directly heated to 180°C at a rate of 1.0°C / minute and held at that temperature for 24 hours. The remaining steps are exactly the same as in Example 1.

[0081] Comparison Example 3: Comparison of Commercially Available Products

[0082] A commercially available nano-boehmite product (brand name C-BM-1) for battery coating was directly selected as the benchmark for performance comparison.

[0083] Performance testing and data analysis

[0084] The nano-boehmite powders obtained in Examples 1-3 and Comparative Examples 1-3 were characterized for their properties. The test results of key indicators are shown in Table 1.

[0085] 1. Sodium content: determined by inductively coupled plasma optical emission spectrometry (ICP-OES).

[0086] 2. Particle size distribution (D50): Determined using a laser particle size analyzer (wet dispersion).

[0087] 3. Specific surface area (BET): Calculated using the nitrogen adsorption-desorption method and the BET model.

[0088] 4. Microscopic morphology: Observed using a scanning electron microscope (SEM).

[0089] Table 1: Performance Test Results of Nano-boehmite Powder

[0090]

[0091] In summary, the sodium content of the products from Examples 1-3 was all below 300 ppm, while the sodium content of Comparative Example 1, which used static calcination, increased to 480 ppm. This comparison confirms the effectiveness of the exhaust mechanism of the dynamic calcination furnace in removing water vapor and reducing impurity content. Furthermore, the particle size of the products from the Examples was concentrated in the range of 88-118 nm with regular morphology. Compared to Comparative Example 2, which used a single hydrothermal process (D50 of 165 nm with significant agglomeration), this demonstrates the effective control of crystal growth by the two-stage hydrothermal synthesis process. Therefore, the process combination of this invention achieves synergistic optimization of product purity, particle size, and morphology.

[0092] Application Validation

[0093] The above materials were used to coat a PE separator (base film thickness 12μm):

[0094] 1. Slurry: Nano boehmite powder: PVDF binder: thickener = 93:4:3 (weight ratio), adjusted with NMP to a slurry with a solid content of 40%.

[0095] 2. Process: Apply the coating to one side of the base film using a doctor blade and dry and cure at 100℃.

[0096] Coated membranes were prepared using the products of Example 1, Comparative Example 1, and Comparative Example 3, respectively, following the same process described above. The performance comparisons are as follows:

[0097]

[0098] The nano-boehmite (such as the product of Example 1) prepared by the method of this invention can form an excellent porous ceramic coating due to its high purity, fine particle size, and good dispersibility, thereby significantly improving the thermal stability, wettability, and strength of the battery separator. This effect is directly derived from the unique preparation process of this invention.

[0099] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing nanooxides, characterized in that, The specific steps are as follows: S1. Raw material calcination activation: Aluminum hydroxide raw material is calcined at 500±10℃ for 1±0.2 hours to obtain activated alumina powder; S2. Preparation of precursor slurry: The alumina powder and pure water are mixed at a solid-liquid ratio of 1:9, a dispersant is added, and the mixture is stirred evenly to form a precursor slurry; S3. Hydrothermal synthesis: The precursor slurry is placed in a reactor and hydrothermal reaction is carried out by programmed temperature increase. First, the temperature is increased to 120±5℃ and held for 12±1 hours, then the temperature is increased to 180±5℃ and held for another 12±1 hours to obtain nano-boehmite slurry. S4. Washing and filtration: The nano-boehmite slurry is washed with pure water and filtered until the pH of the filtrate is ≤8, to obtain nano-boehmite filter cake; S5. Drying and depolymerization: After drying the nano-boehmite filter cake, it is subjected to air-jet milling and depolymerization to obtain nano-boehmite powder; The calcination process in step S1 is carried out in a dynamic calcination furnace, which includes a base (1), a rotating plate (2) rotatably connected to the top of the base (1), an organic body (3) fixedly connected to the top of the rotating plate (2), a kiln body (4) being provided in the inner cavity of the organic body (3), a rotating cover (5) and a discharge cover (6) being provided at the two ends of the kiln body (4), the rotating cover (5) being rotatably connected to the kiln body (4), a toothed ring (13) being fixedly connected to the outer wall of the kiln body (4) near the rotating cover (5), a limiting ring (11) being fixedly connected to the outer wall of the kiln body (4) near the discharge cover (6), a support base (12) being fixedly connected to the top of the rotating plate (2), and the limiting ring (11) being rotatably connected to the support base (12). The inner wall of the kiln body (4) is provided with a feed inlet (7) on one side of the toothed ring (13). The top of the feed inlet (7) is fixedly connected to a cover plate (10) by bolts. The top of the rotating plate (2) is symmetrically fixedly connected to a mounting base (14) below the toothed ring (13). The top of the mounting base (14) is rotatably connected to a first spur gear (15). The outer wall of the toothed ring (13) is provided with a first tooth groove, which meshes with the first spur gear (15). A motor (16) is installed on the outer wall of one of the mounting bases (14). The first spur gear (15) is connected to the output end of the motor (16). The steam in the kiln body (4) is discharged through the exhaust mechanism (8). The discharge cover (6) is automatically moved through the switching mechanism (9). The exhaust mechanism (8) includes a mounting bracket (801), which is fixedly connected to the top of the base (1) and located above the rotating plate (2). An air inlet pipe (802) and an exhaust pipe (803) are fixedly connected to the outer wall of the mounting bracket (801). A connecting cylinder (804) is slidably sleeved at the bottom end of both the air inlet pipe (802) and the exhaust pipe (803). A connecting hole (805) is opened on the outer wall of both the rotating cover (5) and the discharge cover (6). A displacement bracket (806) is fixedly connected to the top of the connecting cylinder (804). A second spur gear (807) is rotatably connected to the inner wall of the mounting bracket (801). The two displacement brackets (806) are in contact with the top and bottom ends of the second spur gear (807) respectively. A hydraulic cylinder (808) is installed inside the base (1). The output end of the hydraulic cylinder (808) is connected to a displacement plate (809). The base (1) has a displacement groove (810) for the displacement plate (809) to slide inside. The base (1) is slidably connected to a vertical plate (812) extending to the bottom of the rotating plate (2). A connecting plate (811) is fixedly connected to the outer wall of the vertical plate (812). The connecting plate (811) is located above the displacement plate (809). The base (1) is slidably connected to a pushing block (813) extending into the cavity of the displacement groove (810). A spring (814) is connected between the pushing block (813) and the base (1). A pushing frame (815) is fixedly connected to the top of the pushing block (813). The pushing frame (815) is fixedly connected to a connecting cylinder (804).

2. The method for preparing nano-boehmite according to claim 1, characterized in that, In step S2, the conductivity of the pure water is <1.1 μS / cm; the dispersant includes sodium polyacrylate and polyethylene glycol, and their addition amounts are 6‰ and 8‰ of the mass of alumina powder, respectively; in step S3, the rate of temperature program is controlled at 1-1.5℃ / min.

3. The method for preparing nano-boehmite according to claim 1, characterized in that, In step S5, the drying temperature is 200±10℃; the particle size D50 of the nano-boehmite powder is 100±20 nanometers, the sodium content is <300 ppm, and the specific surface area is ≤35 m² / g.

4. The method for preparing nano-boehmite according to claim 1, characterized in that, The switching mechanism (9) includes a rotating groove (901) located at the top of the base (1). The rotating plate (2) is located on the inner wall of the rotating groove (901). A fixing rod (902) is fixedly connected to the inner wall of the rotating groove (901). The fixing rod (902) passes through the rotating plate (2). A first bevel gear (903) is symmetrically fixedly connected to the outer wall of the fixing rod (902). The interior of the rotating plate (2) is located on the outer wall of the first bevel gear (903). A geared disc (904) is rotatably connected to the inside of the rotating plate (2), which is located on the outer wall of the geared disc (904). A second bevel gear (905) is rotatably connected to the inside of the rotating plate (2). A connecting shaft (906) is fixedly connected to the top of the second bevel gear (905). A third spur gear (907) is fixedly connected to the top of the connecting shaft (906). A rack (908) is slidably connected to the inside of the support base (12), which is located on the outer wall of the third spur gear (907). The rack (908) is fixedly connected to the discharge cover (6).

5. The method for preparing nano-boehmite according to claim 1, characterized in that, The push block (813) extends to the bottom end of the cavity of the displacement groove (810) and is provided with an inclined surface. The outer wall of the connecting cylinder (804) is in contact with the inner wall of the connecting hole (805).

6. The method for preparing nano-boehmite according to claim 1, characterized in that, The outer wall of the displacement frame (806) is provided with a second tooth groove, which meshes with the second spur gear (807). The inner wall of the mounting frame (801) is fixedly connected with a guide frame (17), and the inner wall of the guide frame (17) is in contact with the outer wall of the displacement frame (806).

7. The method for preparing nano-boehmite according to claim 4, characterized in that, One end of the gear disk (904) is provided with a first gear tooth, which meshes with the first bevel gear (903); the other end of the gear disk (904) is provided with a second gear tooth, which meshes with the second bevel gear (905); the outer wall of the gear rack (908) is provided with a third tooth groove, which meshes with the third spur gear (907).

8. A method for applying nano-boehmite prepared according to any one of claims 1-7 to a lithium-ion battery separator, characterized in that, Includes the following steps: The nano-boehmite powder, binder, and solvent are mixed to prepare a ceramic coating slurry; the ceramic coating slurry is then uniformly coated onto the surface of a polyolefin-based film. After drying and curing, a nano-boehmite ceramic coating is formed on the surface of the base film.

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