Ultrathin heat-resistant coated diaphragm ultrasonic cavitation pulping method

Abstract

The application belongs to the technical field of battery separator, and particularly relates to an ultrasonic cavitation slurry making method for super-thin heat-resistant coated separator. The method comprises the following steps: raw material pretreatment, ceramic particles, a binder and a dispersing agent are added into deionized water to obtain a premix liquid by stirring; ultrasonic cavitation pretreatment, the premix liquid is sent into an ultrasonic cavitation reaction tank, and the initial agglomerates of the ceramic particles are broken by cavitation bubbles generated by ultrasonic waves to obtain a primary dispersed slurry; synergistic fine dispersion, the primary dispersed slurry is sent into a low-speed sand mill for fine dispersion to obtain a fine dispersed slurry; slurry storage, the coating slurry after slurry making is sent into a storage tank for low-speed stirring and storage. The ultrasonic cavitation technology and the low-speed sand mill are synergistically used, the ultrasonic cavitation parameters are accurately matched with the characteristics of the coating separator slurry, the ceramic particles are uniformly and efficiently dispersed, and the high-quality slurry suitable for the super-thin heat-resistant coated separator is prepared.

Description

Technical Field

[0001] This invention relates to the field of battery separator technology, specifically to an ultrasonic cavitation slurry preparation method for an ultrathin heat-resistant coated separator. Background Technology

[0002] The coated separator is one of the core components of a lithium battery. The uniformity and stability of the dispersion of the ceramic slurry (such as alumina, porous alumina, or boehmite slurry) coated on its surface directly determine the coating quality, heat resistance, and ion conduction efficiency of the separator, thus affecting the cycle life, rate performance, and safety performance of the lithium battery. Currently, the slurry preparation process for coated separators mainly adopts traditional sand milling and mechanical stirring methods. These methods have the following technical drawbacks: First, traditional sand milling slurry preparation relies on the impact and shearing action of grinding media such as zirconia beads to disperse materials. Over long-term operation, the grinding media wears down, and the resulting zirconia particles become impurities mixed into the slurry, affecting its purity and particle size distribution uniformity, thus impacting the performance of the coated separator. Simultaneously, some materials may be over-ground during sand milling, leading to particle breakage and disrupting the original particle size distribution. For example, CN113517517B discloses a coating slurry and coating process for lithium battery separators. This patent uses ball milling to prepare the coating slurry, the main components of which include modified ceramic powder and PVDF. However, in this technical solution, the ball milling process relies on the impact and shearing action of the grinding media to disperse materials, which easily leads to impurities from grinding media wear and particle breakage from over-grinding, thus affecting the purity and particle size distribution uniformity of the slurry. Furthermore, the ball milling process easily generates temperature rises, which may cause degradation of components such as binders in the slurry, affecting its stability. In addition, traditional ball milling processes struggle to balance slurry dispersion efficiency and dispersion quality, hindering large-scale mass production.

[0003] Secondly, for nanoscale ceramic particles, traditional sand milling processes struggle to completely break down particle agglomerates. The dispersing ability of traditional sand milling is limited by the size and motion of the grinding media, particularly for D... 50For ceramic particles ≤800 nm, micro-agglomerates may still exist in the slurry after sand milling. These agglomerates can cause a grainy feel on the membrane surface during coating, affecting the membrane's density and interfacial adhesion. For example, CN109546056B discloses a membrane coating liquid and a water-based nano-para-aramid coated membrane. This patent relates to a method for preparing the membrane coating liquid, which uses high-speed shearing and sand milling processes. However, in this technical solution, the sand milling process also suffers from the problem of impurities generated by the wear of the grinding media. Moreover, for nano-sized ceramic particles, sand milling is difficult to completely break up particle agglomerates, resulting in the presence of micro-agglomerates in the slurry. After coating, the membrane surface is prone to a grainy feel, affecting the membrane's density and interfacial adhesion. At the same time, the slurry preparation process requires precise control of parameters such as sand milling speed, flow rate, and pressure, which is difficult to match and has high energy consumption.

[0004] Third, traditional sand milling requires precise control of parameters such as mill speed, flow rate, and pressure, which is difficult to match and results in high energy consumption throughout the process. Furthermore, the high-speed movement and friction of the grinding media during sand milling can easily cause temperature rises, potentially leading to thermal degradation of organic components such as binders in the slurry and affecting its stability.

[0005] Fourth, traditional pulping processes struggle to simultaneously achieve both dispersion efficiency and dispersion quality. Insufficient dispersion results in substandard pulp quality, while prolonged dispersion time impacts production efficiency, hindering large-scale mass production. Furthermore, although ultrasonic cavitation technology has been applied to battery electrode slurry preparation, it has not yet been applied to the large-scale preparation of ceramic slurries for coating separators. Existing ultrasonic pulping technologies suffer from parameter mismatches with the characteristics of coating separator slurries, failing to directly meet the preparation requirements of high solids content, low viscosity, and high particle uniformity in coating separator slurries. For example, CN109860479A discloses a lithium battery separator coating, a separator, and a method for preparing the separator coating. The preparation method of the coating includes the following steps: inorganic particles are added to a solvent and ultrasonically dispersed for 1 hour; after heating to 80-85°C, a modifier and a reaction aid are added; the mixture is mechanically stirred for 4-6 hours; the particles are then separated, washed, and dried to obtain modified inorganic particles; the modified inorganic particles and solvent are mixed in a stirring tank and stirred at 1000 rpm for one hour at room temperature to obtain a uniform dispersion; a binder is added to the uniform dispersion and stirred at 2000 rpm for 2 hours, and then stirred at 500 rpm for 2 hours to obtain the lithium battery separator coating. This method uses ultrasound to disperse inorganic particles in the pretreatment stage, but the subsequent slurry preparation process still relies on mechanical stirring, failing to fully utilize the advantages of ultrasonic cavitation. The ultrasonic parameters (such as frequency, power, and processing time) of this technical solution do not match the characteristics of the diaphragm coating slurry, and cannot be directly applied to the large-scale preparation of diaphragm coating ceramic slurry. Furthermore, this method is not optimized for the high solids content and low viscosity characteristics of the diaphragm coating slurry.

[0006] The aforementioned problems indicate that existing coated diaphragm pulping processes still have certain shortcomings in terms of slurry purity, particle size distribution uniformity, and dispersion efficiency, and still rely heavily on mechanical dispersion. Therefore, this invention provides an ultrasonic cavitation pulping method for ultra-thin heat-resistant coated diaphragms, aiming to achieve efficient and pollution-free slurry dispersion through ultrasonic cavitation technology. This solves the problems of media abrasion, particle agglomeration, and complex parameter control inherent in traditional sand milling pulping, thereby meeting the requirements for uniform dispersion, high efficiency and energy saving, and no impurity contamination in coated diaphragm slurry preparation. Summary of the Invention

[0007] To address the technical problems of traditional sand milling slurry preparation processes, such as grinding media wear and contamination, difficulty in breaking up nanoparticle agglomerations, high energy consumption, and poor slurry stability, this invention provides a method for preparing coated diaphragm slurry using the synergistic effect of ultrasonic cavitation technology and low-speed sand milling. By matching ultrasonic cavitation parameters with the characteristics of the coated diaphragm slurry, efficient and uniform dispersion of ceramic particles is achieved, resulting in a high-quality slurry suitable for ultra-thin heat-resistant coated diaphragms.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a method for ultrasonic cavitation slurry preparation using an ultrathin heat-resistant coated diaphragm, comprising the following steps: Step 1: Raw material pretreatment Weigh the raw material components, which include, by weight: 25-35 parts ceramic particles, 1-3 parts binder, 0.5-1.5 parts dispersant, and 60-70 parts deionized water; Add the accurately weighed binder and dispersant to deionized water, and stir at a low speed of 400-550 r / min to fully dissolve the binder and dispersant. The stirring time is controlled at 10-20 min to obtain a premixed solution. Step 2: Ultrasonic cavitation pretreatment The premixed liquid is fed into an ultrasonic cavitation reaction vessel, and the ultrasonic parameters are set as follows: ultrasonic frequency 15-40kHz, ultrasonic power 300-500W, ultrasonic treatment time 15-30min, while the feed flow rate is controlled at 800-1000L / h; the temperature inside the reaction vessel is controlled at 25-35℃; after the ultrasonic cavitation treatment is completed, a preliminary dispersed slurry is obtained. Step 3: Collaborative, Refined, and Decentralized Management The initially dispersed slurry is fed into a sand mill. The specific parameters of the sand mill are set as follows: spindle speed 300-600 r / min, working pressure of the sand mill chamber 0.1-0.25 MPa, media filling rate 75%-80%, and slurry temperature controlled ≤45℃. Grinding is continued until D is obtained. 50 0.3-0.6μm, D 90 Coating slurry with a thickness ≤1.8μm and a viscosity of 20-150mPa·s; Step 4: Slurry storage The prepared coating slurry is sent to a storage tank, and the storage temperature is controlled at 20-30℃. It is stirred at a low speed of 200-300r / min and stored for later use.

[0009] Preferably, the ceramic particles are one or more of boehmite, alumina, or porous alumina; the initial D of the ceramic particles 50 The thickness is 0.3-0.8 μm; the adhesive is an acrylic adhesive, specifically acrylic acid or acrylic copolymer; the dispersant is an aqueous dispersant such as ammonium acrylate or sodium polyacrylate; the conductivity of the deionized water is controlled below 10 μS / cm.

[0010] As a preferred method, ultrasonic cavitation treatment uses pulsed ultrasound, with the pulse frequency controlled at 1-2 Hz and the duty cycle controlled at 50%-70%.

[0011] Preferably, the grinding media is zirconia beads with a size of 0.6-0.9 mm; the grinding time is 5-10 min.

[0012] The present invention also proposes a method for preparing an ultrathin heat-resistant coated diaphragm using the above-mentioned coating slurry, comprising the following steps: taking out the stored coating slurry, coating it with a 150-800 LPI anilox roller, drying it after coating, and obtaining an ultrathin heat-resistant coated diaphragm.

[0013] Preferably, the coating method is transfer coating or direct coating; the drying temperature is controlled at 80-120℃ and the drying time is 2-5 minutes.

[0014] The present invention also proposes a method for preparing an ultrathin heat-resistant coated diaphragm using the above-mentioned coating slurry.

[0015] The core innovation of this invention lies in: Ultrasonic cavitation pretreatment technology was employed, utilizing cavitation bubbles generated by ultrasonic waves propagating in a liquid to prepare ceramic slurries for coating diaphragms. Extensive experimental verification determined the suitable range of ultrasonic parameters for these slurries. During ultrasonic cavitation, the instantaneous high pressure released by bubble collapse can reach 100-500 MPa, simultaneously generating strong shear forces that effectively break down initial agglomerates of ceramic particles, achieving uniform dispersion of nano-sized particles. Parameter design was optimized for the high solids content and low viscosity characteristics of the coating diaphragm slurry, achieving a perfect match between ultrasonic cavitation technology and diaphragm slurry preparation. The ultrasonic cavitation dispersion method eliminates the need for grinding media, and the subsequent sand mill can utilize a lower grinding rate, i.e., dispersion synergistically with low-speed sand milling. Ultrasonic cavitation pretreatment breaks down large agglomerates, resulting in a pre-dispersed slurry, followed by further dispersing of residual micro-agglomerates through low-speed sand milling, while avoiding over-grinding that could lead to particle breakage. This two-stage dispersion strategy ensures both effective dispersion and improved dispersion efficiency. Furthermore, pulsed ultrasound is used to reduce slurry temperature rise. Pulsed ultrasound with a pulse frequency of 1 to 2 Hz and a duty cycle of 50% to 70% combines ultrasonic action with intermittent operation, effectively reducing the temperature rise of the slurry caused by continuous ultrasound, avoiding thermal degradation of organic components such as binders during the ultrasound process, and ensuring the stability of the slurry.

[0016] Compared to existing technologies, the advantages of this solution are: The ultrasonic cavitation slurry preparation method for ultrathin heat-resistant coated diaphragms provided by this invention achieves efficient and uniform preparation of coated diaphragm ceramic slurry through the synergistic effect of ultrasonic cavitation technology and low-speed sand milling. It solves many technical problems existing in traditional slurry preparation processes and has significant technical advantages and broad application prospects. Attached Figure Description

[0017] Figure 1 This is a SEM image of Example 1; Figure 2 This is the SEM image of Comparative Example 1. Detailed Implementation

[0018] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present application.

[0019] In the technical solution of this invention, the entire pulping process is divided into four main steps: raw material pretreatment, ultrasonic cavitation pretreatment, synergistic fine dispersion, and pulp storage. Each step has specific process parameters and operating conditions, which will be described in detail below.

[0020] General Implementation Examples An ultrasonic cavitation slurry preparation method for an ultrathin heat-resistant coated diaphragm includes the following steps: Step 1: Raw material pretreatment The raw material components, by weight, include: 25-35 parts ceramic particles, 1-3 parts binder, 0.5-1.5 parts dispersant, and 60-70 parts deionized water.

[0021] The specific steps for raw material pretreatment are as follows: Accurately weighed binder and dispersant are added to deionized water, and stirred at a low speed of 400-550 rpm for 10-20 minutes to fully dissolve the binder and dispersant. Then, ceramic particles are added, and stirring and dispersion continues for another 10-20 minutes. During stirring, excessive air bubbles should be avoided to prevent affecting the subsequent ultrasonic cavitation treatment. After stirring, a homogeneous premixed solution is obtained, free of undissolved particles or agglomerates.

[0022] The ceramic particles used in this invention can be one or more of boehmite, alumina, or porous alumina. The initial D of the ceramic particles... 50 The thickness should be 0.3-0.8 μm; the binder can be an acrylic binder, specifically acrylic acid or acrylic copolymers; the dispersant can be an aqueous dispersant such as ammonium acrylate or sodium polyacrylate; the conductivity of deionized water should be controlled below 10 μS / cm to ensure water purity and avoid impurities affecting the slurry performance.

[0023] Step 2: Ultrasonic cavitation pretreatment The ultrasonic cavitation pretreatment uses an ultrasonic cavitation reactor, which is equipped with an ultrasonic generator, a jacketed cooling system, a feed pump, and a temperature control system. Essentially, it utilizes the cavitation effect generated by ultrasonic waves propagating in a liquid to achieve the initial dispersion of ceramic particles. The volume of the ultrasonic cavitation reactor can be selected according to the production scale.

[0024] The specific steps for ultrasonic cavitation pretreatment are as follows: The premixed liquid obtained in step one is fed into an ultrasonic cavitation reactor via a feed pump. The ultrasonic generator is turned on, and the ultrasonic parameters are set as follows: ultrasonic frequency 15-40kHz, ultrasonic power 300-500W, ultrasonic treatment time 15-30min, while the feed flow rate is controlled at 800-1000L / h. The ultrasonic cavitation treatment uses pulsed ultrasound, with the pulse frequency controlled at 1-2Hz and the duty cycle controlled at 50%-70%. The temperature inside the reactor is controlled at 25-35℃, and the inlet pressure of the cooling water is controlled at 0.2-0.3MPa. After the ultrasonic cavitation treatment is completed, a preliminary dispersed slurry is obtained.

[0025] During ultrasonic cavitation, ultrasonic waves propagate through the premixed liquid, generating periodically changing negative and positive pressures. Under negative pressure, tiny bubble nuclei form in the liquid, which rapidly expand and collapse under subsequent positive pressure. The collapse of these bubble nuclei generates instantaneous high pressures, reaching 100-500 MPa, along with strong shear forces and jets. These physical effects act on the ceramic particles, effectively breaking down initial agglomerates and achieving preliminary dispersion. The advantage of pulsed ultrasound is that it reduces the temperature rise of the slurry caused by continuous ultrasound, preventing thermal degradation of organic components such as binders and dispersants in the slurry system. The ultrasonic cavitation reactor is equipped with a jacketed cooling system, which controls the temperature within the reactor within a set range by circulating cooling water.

[0026] After ultrasonic cavitation treatment, most of the ceramic particle agglomerates in the slurry have been broken up and the particles have been initially dispersed, but a small number of tiny agglomerates may still exist, requiring further processing in subsequent steps.

[0027] Step 3: Collaborative, Refined, and Decentralized Management The collaborative fine dispersion step uses a low-speed sand mill to further refine the dispersion of the initially dispersed slurry. The purpose of this step is to break down any remaining micro-agglomerates while avoiding over-grinding that could lead to particle breakage.

[0028] The equipment used for collaborative fine dispersion is a horizontal sand mill, which is equipped with a main shaft, sand grinding chamber, grinding media, cooling system, air sealing system and pressure control system.

[0029] The initially dispersed slurry is fed into a low-speed sand mill for fine dispersion. The specific parameters of the sand mill are set as follows: spindle speed 300-600 r / min, sand mill chamber working pressure 0.1-0.25 MPa, and media filling rate 75%-80%. The grinding media are zirconia beads with a media size of 0.6-0.9 mm. The sand milling time is 5-10 min. The external connection parameters of the sand mill include: external compressed air pressure 0.4-0.5 MPa, mechanical seal air seal pressure 0.30-0.35 MPa, and cooling water inlet pressure 0.20-0.25 MPa. During the sand milling process, the slurry temperature needs to be controlled ≤45℃. Cooling water circulates through the sand mill's cooling system to remove the heat generated during the sand milling process, preventing the slurry temperature from becoming too high and causing degradation of organic components such as binders.

[0030] After the collaborative fine dispersion step is completed, a finely dispersed slurry, i.e., a coating slurry, is obtained. At this point, the ceramic particles in the coating slurry are fully dispersed and have a uniform particle size distribution. Sampling and testing of the coating slurry D... 50 0.3-0.6μm, D 90 ≤1.8μm, and viscosity is 20-150mPa·s.

[0031] Step 4: Slurry storage The purpose of the slurry storage step is to maintain the stability of the slurry and prevent sedimentation and agglomeration during storage.

[0032] The slurry is stored in a storage tank equipped with a temperature control system and a low-speed stirring device. The specific operating steps are as follows: The prepared coating slurry is transferred to the storage tank. The storage tank is equipped with a temperature control system to maintain the storage temperature at 20-30℃; the storage tank is also equipped with a low-speed stirring device, which is used to prevent slurry sedimentation and agglomeration, with the stirring speed controlled at 200-300 r / min. During storage, parameters such as viscosity and particle size of the slurry should be monitored regularly to ensure stable slurry performance.

[0033] Preparation process of ultra-thin heat-resistant coated diaphragm: The stored slurry is taken out and coated using a conventional line count (150-800 LPI) anilox roller. The coating method can be transfer coating or direct coating, selected according to the characteristics of the diaphragm substrate. After coating, the diaphragm enters a drying process, with the drying temperature controlled at 80-120℃ and the drying time controlled at 2-5 minutes. After drying, an ultra-thin, heat-resistant coated diaphragm is obtained.

[0034] Example 1 An ultrasonic cavitation slurry preparation method for an ultrathin heat-resistant coated diaphragm includes the following steps: 1. Premixing: Weigh 25 parts by weight of boehmite particles (initial D) 50The mixture consists of 0.65 μm of a binder (acrylic acid), 2 parts of a dispersant (ammonium acrylate), 1 part of a dispersant, and 65 parts of deionized water. The binder and dispersant are added to the deionized water and stirred at 500 r / min for 15 min. Then, ceramic particles are added and the mixture is stirred and dispersed for another 15 min.

[0035] 2. Ultrasonic cavitation pretreatment: The premixed liquid is fed into the ultrasonic cavitation reaction vessel through a feed pump. The ultrasonic generator is turned on, and the ultrasonic parameters are set as follows: ultrasonic frequency 30kHz, ultrasonic power 400W, pulse frequency 1.5Hz, duty cycle 60%, ultrasonic treatment time 20min, and the feed flow rate is controlled at 900L / h. Cooling water is introduced through the jacket to control the temperature inside the reaction vessel at 30℃, thus obtaining a preliminary dispersed slurry.

[0036] 3. Collaborative Refined Dispersion: The initially dispersed slurry is fed into a horizontal sand mill, and the sand milling parameters are set as follows: spindle speed 500 r / min, working pressure of the sand milling chamber 0.2 MPa, external compressed air pressure 0.5 MPa, mechanical seal air seal pressure 0.35 MPa, cooling water inlet pressure 0.25 MPa; the grinding media is zirconia beads with a media size of 0.6-0.9 mm and a filling rate of 78%; the sand milling time is 8 min; and the slurry temperature is controlled to be ≤40℃ during the sand milling process to obtain a refined dispersed slurry.

[0037] 4. Slurry storage: The prepared coating slurry is sent to a storage tank, the storage temperature is controlled at 25℃, and it is stirred at a low speed of 300rpm. It is kept warm and stored for later use.

[0038] An ultrathin heat-resistant coated separator was prepared by direct coating using a 600 LPI anilox roller, followed by drying at 90°C for 3 minutes to obtain a double-sided coated separator. The microstructure characterized by SEM is shown in the figure. Figure 1 As shown in the figure, the membrane prepared in Example 1 is smooth and free of obvious particulate matter.

[0039] Example 2 An ultrasonic cavitation slurry preparation method for an ultrathin heat-resistant coated diaphragm includes the following steps: 1. Premixing: Weigh 30 parts by weight of alumina granules (initial D) 50 The mixture consists of 0.72 μm of ceramic particles, 1.5 parts of binder (acrylic copolymer), 0.8 parts of dispersant (sodium polyacrylate), and 67.7 parts of deionized water. The binder and dispersant are added to the deionized water and stirred at 480 r / min for 15 min. Then ceramic particles are added and the mixture is stirred and dispersed for another 15 min to obtain a premixed solution.

[0040] 2. Ultrasonic cavitation pretreatment: The premixed liquid is fed into the ultrasonic cavitation reaction vessel through a feed pump. The ultrasonic generator is turned on and the ultrasonic parameters are set as follows: ultrasonic frequency 25kHz, ultrasonic power 350W, pulse frequency 1Hz, duty cycle 55%, ultrasonic treatment time 25min, and the feed flow rate is controlled at 850L / h. Cooling water is introduced through the jacket to control the temperature inside the reaction vessel at 28℃, thus obtaining a preliminary dispersed slurry.

[0041] 3. Collaborative Refined Dispersion: The initially dispersed slurry is fed into a horizontal sand mill, and the sand milling parameters are set as follows: spindle speed 550 r / min, working pressure of the sand milling chamber 0.18 MPa, external compressed air pressure 0.45 MPa, mechanical seal air seal pressure 0.32 MPa, and cooling water inlet pressure 0.22 MPa; the grinding media is zirconia beads with a media size of 0.6-0.9 mm and a filling rate of 76%; the sand milling time is 7 min; and the slurry temperature is controlled to be ≤45℃ during the sand milling process to obtain a refined dispersed slurry.

[0042] 4. Slurry storage: The prepared coating slurry is sent to a constant temperature storage tank, the storage temperature is controlled at 22℃, and it is stirred at a low speed of 300r / min. It is kept warm and stored for later use.

[0043] An ultra-thin heat-resistant coated diaphragm is prepared by coating: a 600 LPI anilox roller is used for direct coating, and the diaphragm is dried at 90°C for 3 minutes to obtain a double-sided coated diaphragm.

[0044] Example 3 An ultrasonic cavitation slurry preparation method for an ultrathin heat-resistant coated diaphragm includes the following steps: 1. Premixing: Weigh 30 parts by weight of boehmite particles (initial D) 50 The mixture consists of 0.65 μm of ceramic particles, 2.5 parts of binder (acrylic copolymer), 1.5 parts of dispersant (sodium polyacrylate), and 66 parts of deionized water. The binder and dispersant are added to the deionized water and stirred at 480 r / min for 15 min. Then, ceramic particles are added and stirred and dispersed for another 15 min until no obvious bubbles are observed.

[0045] 2. Ultrasonic cavitation pretreatment: The premixed liquid is fed into the ultrasonic cavitation reaction vessel through a feed pump. The ultrasonic generator is turned on, and the ultrasonic parameters are set as follows: ultrasonic frequency 20kHz, ultrasonic power 450W, pulse frequency 1.5Hz, duty cycle 65%, ultrasonic treatment time 20min, and feed flow rate controlled at 900L / h. Cooling water is introduced through the jacket to control the temperature inside the reaction vessel at 30℃ and the cooling water inlet pressure at 0.25MPa, thus obtaining a preliminary dispersed slurry.

[0046] 3. Collaborative Refined Dispersion: The initially dispersed slurry is fed into a horizontal sand mill, and the sand milling parameters are set as follows: spindle speed 450 r / min, working pressure of the sand milling chamber 0.20 MPa, external compressed air pressure 0.45 MPa, mechanical seal air seal pressure 0.33 MPa, cooling water inlet pressure 0.22 MPa; the grinding media is zirconia beads with a media size of 0.6-0.9 mm and a filling rate of 78%; the sand milling time is 8 min; and the slurry temperature is controlled to be ≤42℃ during the sand milling process to obtain a refined dispersed slurry.

[0047] 4. Slurry storage: The prepared coating slurry is sent to a storage tank, the storage temperature is controlled at 25℃, and it is stirred at a low speed of 250r / min. It is kept warm and stored for later use.

[0048] An ultra-thin heat-resistant coated diaphragm is prepared by coating: a 600 LPI anilox roller is used for direct coating, and the diaphragm is dried at 100°C for 3.5 minutes to obtain a double-sided coated diaphragm.

[0049] Example 4 An ultrasonic cavitation slurry preparation method for an ultrathin heat-resistant coated diaphragm includes the following steps: 1. Premixing: Weigh 32 parts by weight of alumina granules (initial D) 50 The mixture consists of 0.60 μm of ceramic particles, 2 parts of binder (acrylic acid), 0.8 parts of dispersant (ammonium acrylate), and 65.2 parts of deionized water. The binder and dispersant are added to the deionized water and stirred at 500 r / min for 18 min. Then, ceramic particles are added and the mixture is stirred and dispersed for another 15 min.

[0050] 2. Ultrasonic cavitation pretreatment: The premixed liquid is fed into the ultrasonic cavitation reaction vessel through a feed pump. The ultrasonic generator is turned on, and the ultrasonic parameters are set as follows: ultrasonic frequency 35kHz, ultrasonic power 400W, pulse frequency 1.8Hz, duty cycle 58%, ultrasonic treatment time 22min, and the feed flow rate is controlled at 950L / h. Cooling water is introduced through the jacket to control the temperature inside the reaction vessel at 28℃ and the cooling water inlet pressure at 0.28MPa, thus obtaining a preliminary dispersed slurry.

[0051] 3. Collaborative Refined Dispersion: The initially dispersed slurry is fed into a horizontal sand mill, and the sand milling parameters are set as follows: spindle speed 550 r / min, working pressure of the sand milling chamber 0.22 MPa, external compressed air pressure 0.48 MPa, mechanical seal air seal pressure 0.34 MPa, and cooling water inlet pressure 0.23 MPa; the grinding media is zirconia beads with a media size of 0.6-0.9 mm and a filling rate of 76%; the sand milling time is 7 min; and the slurry temperature is controlled to be ≤40℃ during the sand milling process to obtain a refined dispersed slurry.

[0052] 4. Slurry storage: The prepared coating slurry is sent to a storage tank, the storage temperature is controlled at 22℃, and it is stirred at a low speed of 280r / min. It is kept warm and stored for later use.

[0053] An ultra-thin heat-resistant coated diaphragm is prepared by coating: a 500 LPI anilox roller is used for direct coating, and the diaphragm is dried at 110°C for 2.5 minutes to obtain a double-sided coated diaphragm.

[0054] Example 5 An ultrasonic cavitation slurry preparation method for an ultrathin heat-resistant coated diaphragm includes the following steps: 1. Premixing: Weigh 35 parts by weight of porous alumina particles (initial D) 50 The mixture consists of 0.40 μm of ceramic particles, 3 parts of binder (acrylic copolymer), 1.2 parts of dispersant (sodium polyacrylate), and 60.8 parts of deionized water. The binder and dispersant are added to the deionized water and stirred at 420 r / min for 20 min. Then, ceramic particles are added and the mixture is stirred and dispersed for another 15 min to obtain a premixed solution.

[0055] 2. Ultrasonic cavitation pretreatment: The premixed liquid is fed into the ultrasonic cavitation reaction vessel through a feed pump. The ultrasonic generator is turned on, and the ultrasonic parameters are set as follows: ultrasonic frequency 40kHz, ultrasonic power 500W, pulse frequency 2.0Hz, duty cycle 70%, ultrasonic treatment time 18min, and feed flow rate controlled at 1000L / h. Cooling water is introduced through the jacket to control the temperature inside the reaction vessel at 32℃ and the cooling water inlet pressure at 0.30MPa, thus obtaining a preliminary dispersed slurry.

[0056] 3. Collaborative Refined Dispersion: The initially dispersed slurry is fed into a horizontal sand mill, and the sand milling parameters are set as follows: spindle speed 350 r / min, working pressure of the sand milling chamber 0.15 MPa, external compressed air pressure 0.50 MPa, mechanical seal air seal pressure 0.35 MPa, and cooling water inlet pressure 0.25 MPa; the grinding media is zirconia beads with a media size of 0.6-0.9 mm and a filling rate of 80%; the sand milling time is 10 min; and the slurry temperature is controlled to be ≤45℃ during the sand milling process to obtain a refined dispersed slurry.

[0057] 4. Slurry storage: The prepared coating slurry is sent to a storage tank, the storage temperature is controlled at 28℃, and it is stirred at a low speed of 220r / min. It is kept warm and stored for later use.

[0058] An ultra-thin heat-resistant coated diaphragm is prepared by coating: a 700 LPI anilox roller is used for direct coating, and the diaphragm is dried at 80°C for 5 minutes to obtain a double-sided coated diaphragm.

[0059] Comparative Example 1 The coating slurry was prepared using a traditional sand milling process, with the raw material ratios consistent with Example 1. The mixed materials were directly fed into a sand mill for dispersion and grinding. The milling parameters were: spindle speed 900 r / min, feed flow rate 900 L / h, milling chamber working pressure 0.20 MPa, media filling rate 78%, and milling time 30 min. The resulting coating slurry was directly coated using a 600 LPI anilox roller and dried at 90°C for 3 min to obtain a double-sided coated diaphragm. The microstructure characterized by SEM is shown below. Figure 2 As shown in the figure, the membrane prepared in Comparative Example 1 has obvious granular protrusions.

[0060] Comparative Example 2 The coating slurry was prepared using a traditional sand milling process, with the same raw material ratio as in Example 2. The mixed materials were directly fed into a sand mill for dispersion and grinding. The sand milling parameters were: spindle speed 900 r / min, feed flow rate 900 L / h, working pressure of the sand milling chamber 0.20 MPa, media filling rate 78%, and sand milling time 30 min. The resulting coating slurry was then directly coated using a 600 LPI anilox roller and dried at 90°C for 3 min to obtain a double-sided coated diaphragm.

[0061] Comparative Example 3 The only difference from Example 1 is that in step 2, ultrasonic cavitation pretreatment: the premixed liquid is sent into the ultrasonic cavitation reaction vessel, and the ultrasonic parameters are set: ultrasonic power 550W, and the other parameters are the same as in Example 1.

[0062] Comparative Example 4 The only difference from Example 1 is that in step 2, ultrasonic cavitation pretreatment: the premixed liquid is sent into the ultrasonic cavitation reaction vessel, and the ultrasonic parameters are set: ultrasonic frequency 45kHz, and the other parameters are the same as in Example 1.

[0063] Comparative Example 5 The only difference from Example 1 is that in step 2, during the ultrasonic cavitation pretreatment, the temperature inside the reaction vessel is controlled at 40°C, while the other parameters are the same as in Example 1.

[0064] Comparative Example 6 The only difference from Example 1 is that in step 2, during the ultrasonic cavitation pretreatment, the pulse frequency is 2.5 Hz, while the other parameters are the same as in Example 1.

[0065] Comparative Example 7 The only difference from Example 1 is that in step 2, during the ultrasonic cavitation pretreatment, continuous ultrasound is used instead of pulsed ultrasound, i.e., the duty cycle is 0%. The other parameters are the same as in Example 1.

[0066] Comparative Example 8 The difference from Example 1 is that the low-speed sand mill treatment process is replaced with the ultrasonic cavitation pretreatment process: An ultrasonic cavitation slurry preparation method for an ultrathin heat-resistant coated diaphragm includes the following steps: 1. Premixing: Weigh 25 parts by weight of boehmite particles (initial D) 50 The mixture consists of 0.65 μm of ceramic particles, 2 parts of binder (acrylic acid), 1 part of dispersant (ammonium acrylate), and 65 parts of deionized water. The binder and dispersant are added to the deionized water and stirred at 500 r / min for 15 min. Then, ceramic particles are added and the mixture is stirred and dispersed for another 15 min to obtain a premixed solution.

[0067] 2. Ultrasonic cavitation pretreatment: The premixed liquid is fed into a horizontal sand mill via a feed pump. The sand milling parameters are set as follows: spindle speed 500 r / min, working pressure of the sand milling chamber 0.2 MPa, external compressed air pressure 0.5 MPa, mechanical seal air seal pressure 0.35 MPa, and cooling water inlet pressure 0.25 MPa. The grinding media is zirconia beads with a size of 0.6-0.9 mm and a filling rate of 78%. The sand milling time is 8 min. The slurry temperature is controlled to be ≤40℃ during the sand milling process to obtain a preliminary dispersed slurry.

[0068] 3. Collaborative fine dispersion: The initially dispersed slurry is fed into an ultrasonic cavitation reaction vessel, the ultrasonic generator is turned on, and the ultrasonic parameters are set as follows: ultrasonic frequency 30kHz, ultrasonic power 400W, pulse frequency 1.5Hz, duty cycle 60%, ultrasonic treatment time 20min, and the feed flow rate is controlled at 900L / h; cooling water is introduced through the jacket to control the temperature inside the reaction vessel at 30℃, thus obtaining a finely dispersed slurry.

[0069] 4. Slurry storage: The prepared coating slurry is sent to a storage tank, the storage temperature is controlled at 25℃, and it is stirred at a low speed of 300rpm. It is kept warm and stored for later use.

[0070] An ultra-thin heat-resistant coated diaphragm is prepared by coating: a 600 LPI anilox roller is used for direct coating, and the diaphragm is dried at 90°C for 3 minutes to obtain a double-sided coated diaphragm.

[0071] Comparative Example 9 The only difference from Example 1 is that in step 3, during the coordinated fine dispersion process, the spindle speed of the sand mill is 700 r / min, while the other parameters are the same as in Example 1.

[0072] The particle size distribution of the slurries prepared in the examples and comparative examples was tested using a laser particle size analyzer. The test results are shown in Table 1. Table 1. Particle size distribution test results for the examples and comparative examples.

[0073] The thermal shrinkage properties of the coated diaphragms prepared in the examples and comparative examples were tested. Test conditions: the films were kept at 150°C for 1 hour and at 180°C for 0.5 hours, respectively, and the thermal shrinkage rates in the MD and TD directions were measured. The test results are shown in Table 2. Table 2. Test results of heat shrinkage performance of the examples and comparative examples.

[0074] The coated diaphragms prepared in the examples and comparative examples were subjected to electrical performance tests. The capacity retention rate was tested after 500 cycles according to GB / T 18287-2013, and the internal resistance and rate performance were tested according to GB / T 31486-2015. The results are shown in Table 3.

[0075] Table 3. Electrical performance test results of the examples and comparative examples.

[0076] Based on the data in Tables 1 to 3, it can be confirmed that the embodiments of the present invention are significantly superior to the comparative examples in terms of particle size distribution, thermal shrinkage performance, and electrical properties. The technical background of this invention points out that traditional sand milling pulping suffers from problems such as impurities introduced by grinding media abrasion, difficulty in breaking up nanoparticle agglomerations, complex parameter control, and binder degradation due to temperature rise. The method of ultrasonic cavitation pretreatment combined with low-speed sand milling is designed to solve these defects. Analysis of the variation patterns in the data of the embodiments shows that from Embodiment 1 to Embodiment 5, as the ultrasonic frequency, power, time, and sand milling speed are adjusted within the range of the overall embodiments, the D of the pulp... 50 and D 90 All parameters remain stable within a small range, with generally low thermal shrinkage rates and high cycle capacity retention and rate performance. This advantage stems from the instantaneous high pressure and strong shear force generated by bubble collapse during ultrasonic cavitation, which effectively breaks down the initial agglomerates of ceramic particles without media wear contamination. Combined with low-speed sand milling to eliminate residual micro-agglomerates, excessive grinding and temperature rise are avoided, thereby obtaining a uniform and stable slurry, which in turn improves the membrane's density, heat resistance and ion conduction efficiency.

[0077] Comparative analysis of performance differences between the examples and comparative examples: Comparative Example 1 uses a traditional single sand milling process without ultrasonic cavitation pretreatment. The high-speed collision of the grinding media generates more impurities and the particle agglomerates are not completely broken, resulting in a wide particle size distribution, large thermal shrinkage, and low cycle retention rate. Comparative Example 2 also uses traditional sand milling, and the situation is similar to Comparative Example 1, but the effect is significantly worse than that of Example 2. Comparative Example 3 increases the ultrasonic power to 550W, which exceeds the scope of this invention. The excessively high power causes excessively intense cavitation bubbles, which may cause local temperature rise and excessive particle breakage, thus destroying the particle size uniformity. Therefore, the performance is not as good as that of Example 1. Comparative Example 4 uses an ultrasonic frequency of 45kHz, which exceeds the 15-40kHz range. The excessively high frequency makes the cavitation bubble size too small and the collapse energy insufficient, making it difficult to effectively break agglomerates and reducing the dispersion effect. Comparative Example 5 controls the temperature at 40℃ during ultrasonic treatment, which is higher than the 25-35℃ range of this invention. The temperature rise accelerates the thermal degradation of organic components such as binders, affecting the stability of the slurry and the coating quality, resulting in thermal shrinkage and deterioration of electrical properties. Comparative Example 6 uses a pulse frequency of 2.5Hz, exceeding the 1-2Hz range. This excessively high frequency results in insufficient bubble growth and collapse cycles, weakened cavitation, and reduced dispersion efficiency. Comparative Example 7 uses continuous ultrasound instead of pulsed ultrasound, lacking an intermittent cooling phase. This leads to a significant temperature rise in the slurry, easy degradation of the binder, and potential over-dispersion and re-agglomeration of particles, resulting in significant performance degradation. Comparative Example 8 reverses the sequence of sand milling and ultrasound (sand milling followed by ultrasound). In this case, large agglomerates are not pre-broken during sand milling, resulting in a high grinding media load, excessive heat generation, and easy introduction of impurities. Subsequent ultrasound is insufficient to completely eliminate the formed hard agglomerates, thus the effect is not as good as the synergistic sequence of ultrasound followed by sand milling. Comparative Example 9 uses a sand mill spindle speed of 700 r / min, exceeding the 300-600 r / min range. This excessive speed leads to excessive impact force of the grinding media on the particles, easily causing particle breakage and media wear. Simultaneously, it exacerbates the temperature rise, reduces slurry particle size uniformity, and results in thermal shrinkage and electrical properties inferior to Example 1. In summary, the present invention ensures high slurry quality in principle by precisely matching ultrasonic cavitation parameters, using pulsed ultrasound in conjunction with low-speed sand milling, and strictly controlling temperature and process sequence. In contrast, the comparative example suffers from decreased dispersion effect or slurry stability due to deviation from any key parameter, resulting in overall inferiority to the example in terms of particle size, thermal shrinkage, and electrical properties.

[0078] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary; within the framework of this invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

[0079] This invention is intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for ultrasonic cavitation pulping using an ultrathin heat-resistant coated diaphragm, characterized in that, Includes the following steps: Step 1: Raw material pretreatment Weigh the raw material components, which include, by weight: 25-35 parts ceramic particles, 1-3 parts binder, 0.5-1.5 parts dispersant, and 60-70 parts deionized water; Accurately weighed binder and dispersant are added to deionized water and stirred at a low speed of 400-550 r / min to fully dissolve the binder and dispersant. Then ceramic particles are added and dispersed evenly to obtain a premixed solution. Step 2: Ultrasonic cavitation pretreatment The premixed liquid is fed into an ultrasonic cavitation reaction vessel, and the ultrasonic parameters are set as follows: ultrasonic frequency 15-40kHz, ultrasonic power 300-500W, ultrasonic treatment time 15-30min, while the feed flow rate is controlled at 800-1000L / h; the temperature inside the reaction vessel is controlled at 25-35℃; after the ultrasonic cavitation treatment is completed, a preliminary dispersed slurry is obtained. Step 3: Collaborative, Refined, and Decentralized Management The initially dispersed slurry is fed into a sand mill. The specific parameters of the sand mill are set as follows: spindle speed 300-600 r / min, working pressure of the sand mill chamber 0.1-0.25 MPa, media filling rate 75%-80%, and slurry temperature controlled ≤45℃. Grinding is continued until D is obtained. 50 0.3-0.6μm, D 90 Coating slurry with a thickness ≤1.8μm and a viscosity of 20-150mPa·s; Step 4: Slurry storage The prepared coating slurry is sent to a storage tank, and the storage temperature is controlled at 20-30℃. It is stirred at a low speed of 200-300r / min and stored for later use.

2. The ultrasonic cavitation slurry preparation method for an ultrathin heat-resistant coated diaphragm as described in claim 1, characterized in that, The ceramic particles are one or more of boehmite, alumina, or porous alumina; the initial D of the ceramic particles 50 The thickness is 0.3-0.8 μm.

3. The ultrasonic cavitation slurry preparation method for an ultrathin heat-resistant coated diaphragm as described in claim 1, characterized in that, The adhesive is an acrylic adhesive; the dispersant is an ammonium acrylate or sodium polyacrylate.

4. The ultrasonic cavitation slurry preparation method for an ultrathin heat-resistant coated diaphragm as described in claim 1, characterized in that, The conductivity of the deionized water is controlled to be below 10 μS / cm.

5. The ultrasonic cavitation slurry preparation method for an ultrathin heat-resistant coated diaphragm as described in claim 1, characterized in that, The ultrasonic cavitation treatment uses pulsed ultrasound, with the pulse frequency controlled at 1-2 Hz and the duty cycle controlled at 50%-70%.

6. The ultrasonic cavitation slurry preparation method for an ultrathin heat-resistant coated diaphragm as described in claim 1, characterized in that, The grinding media are zirconia beads with a size of 0.6-0.9 mm; the grinding time is 5-10 min.

7. A method for preparing an ultrathin heat-resistant coated diaphragm, characterized in that, Includes the following steps: Take out the coating slurry prepared by the ultrasonic cavitation slurry preparation method for ultra-thin heat-resistant coated diaphragms as described in any one of claims 1-6, apply it with a 150-800 LPI anilox roller, and dry it after coating to obtain an ultra-thin heat-resistant coated diaphragm.

8. The method for preparing the ultrathin heat-resistant coated diaphragm as described in claim 7, characterized in that, The coating method is transfer coating or direct coating; the drying temperature is controlled at 80-120℃ and the drying time is 2-5 minutes.

9. An ultrathin heat-resistant coated diaphragm, characterized in that, The ultrathin heat-resistant coated diaphragm is prepared by the method described in any one of claims 7-8.

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