Ceramic slurry for battery diaphragm as well as preparation method and application of ceramic slurry

Abstract

The invention discloses ceramic slurry for a battery diaphragm as well as a preparation method and application of the ceramic slurry in the field of lithium ion battery materials. The slurry comprises ceramic particles, organosiloxane containing an epoxy group-allyl bifunctional group, organosiloxane containing an isocyanate group-amino bifunctional group, a dispersing agent, a binder and a solvent. The two kinds of modified organosiloxane are prepared through the reaction of 3-chloropropyl trimethoxy silane with allyl alcohol and epoxy chloropropane and the reaction of gamma-aminopropyl trimethoxy silane with isophorone diisocyanate and ethidene diamine respectively, and the two kinds of modified organosiloxane are prepared through the reaction of 3-chloropropyl trimethoxy silane with allyl alcohol and epoxy chloropropane and the reaction of gamma-aminopropyl trimethoxy silane with isophorone diisocyanate and ethidene diamine respectively. The preparation method comprises the following steps: dispersing the ceramic particles in the solvent, adding the dispersant and the binder, stirring at a low speed, adjusting the pH value, sequentially adding the two modifiers, heating, stirring at a high speed, and adjusting the solid content. The obtained ceramic slurry can improve the interface bonding force between a ceramic layer and a polyolefin base material and improve the dispersion stability and heat resistance, and is suitable for preparation of a lithium ion battery diaphragm.

Description

Technical Field

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

[0002] Lithium-ion batteries, as the most promising secondary energy storage devices, are widely used in electric vehicles, portable electronic devices, and large-scale energy storage systems. Improving their performance is crucial for driving the development of the new energy industry. The battery separator, as one of the core components of a lithium-ion battery, plays a vital role in separating the positive and negative electrodes, allowing lithium-ion transport, and preventing electronic short circuits. Its performance directly affects the battery's safety, cycle life, and energy density. Currently, the mainstream lithium-ion battery separators on the market are made of polyolefin materials. These materials have long held a dominant market position due to their lower production costs, excellent chemical stability, and good mechanical strength. However, the inherent defects of polyolefin separators limit their further application in high-performance batteries: on the one hand, their heat resistance is insufficient, and they are prone to thermal shrinkage or even melting under overcharging, short circuits, or high-temperature environments, leading to direct contact between the positive and negative electrodes and causing short circuits, seriously affecting battery safety; on the other hand, polyolefin materials have low surface energy and strong hydrophobicity, resulting in poor wettability with the electrolyte. This leads to insufficient electrolyte retention in the separator, which not only reduces ion transport efficiency but also exacerbates side reactions at the electrode-separator interface, shortening the battery's cycle life.

[0003] To address the aforementioned issues with polyolefin separators, researchers proposed preparing ceramic-coated separators by coating the surface of a polyolefin substrate with ceramic particles. The ceramic particles possess extremely high heat resistance, effectively improving the thermal shrinkage performance of the separator. Furthermore, the polar groups on their surface can form hydrogen bonds with the electrolyte, significantly improving the separator's wettability to the electrolyte. Simultaneously, the ceramic layer can physically block the penetration of lithium dendrites, further enhancing battery safety. However, the preparation of existing ceramic slurries still faces multiple technical challenges: First, the surface of ceramic particles is usually rich in polar hydroxyl groups, which differs greatly from the surface energy of hydrophobic polyolefin substrates, resulting in poor interfacial compatibility and easy coating peeling during use, with a significant increase in interfacial impedance. Second, traditional modifiers are mostly single-functional group structures, which can only partially block the hydroxyl groups on the ceramic surface or achieve simple physical adsorption with the substrate, making it difficult to simultaneously meet the dual requirements of "surface polarity regulation" and "chemical bonding enhancement", thus limiting the improvement of interfacial bonding. Third, ceramic particles are prone to agglomeration due to their high surface energy, and traditional dispersants are not effective at dispersing them. After the slurry is left to stand, sedimentation is likely to occur, leading to uneven coating thickness and decreased density during the coating process, ultimately affecting the stability and consistency of battery performance.

[0004] To address the aforementioned technical bottlenecks, developing novel surface modifiers and matching ceramic slurries is crucial for improving the overall performance of ceramic-coated separators. While existing research attempts to improve interfacial bonding and dispersibility by introducing multifunctional modifiers or optimizing dispersion processes, several shortcomings remain: some bifunctional modifiers, although acting simultaneously on both the ceramic surface and the polymer substrate, have demanding functional group reaction conditions, easily leading to damage to the ceramic particle structure or deterioration of the polyolefin substrate performance; others, while improving slurry dispersibility, fail to effectively enhance interfacial bonding, resulting in low peel strength between the ceramic layer and the substrate, which is insufficient to meet the requirements of high-performance batteries. Therefore, designing multifunctional modifiers that combine "surface hydroxyl blocking - polymer interface grafting - dispersion stability improvement" to synergistically optimize the surface properties of ceramic particles and slurry dispersibility has become a pressing technical problem in this field. This invention, through the design of two novel organosiloxane modifiers, synergistically solves the interfacial compatibility and dispersion stability problems between ceramic particles and polyolefin substrates, providing a new technical path for the preparation of high-performance ceramic-coated separators. Summary of the Invention

[0005] The purpose of this invention is to provide a ceramic slurry for battery separators, its preparation method and application, which solves the technical problems of existing ceramic slurries, such as weak interfacial bonding between ceramic particles and polyolefin substrate, poor dispersion stability, high heat shrinkage rate and insufficient electrolyte wettability.

[0006] The present invention achieves the above objectives through the following technical solutions: A ceramic slurry, comprising the following raw materials in parts by weight: Ceramic particles: 500-800 parts by weight; Organosiloxanes containing epoxy-allyl bifunctional groups: 50-150 parts by weight; Organosiloxanes containing isocyanate-amino bifunctional groups: 30-100 parts by weight; Dispersant: 10-50 parts by weight; Adhesive: 20-80 parts by weight; Solvent: 10-30 parts by weight; The method for preparing the organosiloxane containing the epoxy-allyl bifunctional group includes: A1, adding 3-chloropropyltrimethoxysilane and allyl alcohol to anhydrous tetrahydrofuran and stirring evenly under nitrogen protection; adding sodium hydroxide and heating to 60-70℃ for reaction, removing the generated water through a water separator during the reaction; after the reaction is completed, distilling under reduced pressure to obtain 3-chloropropylallyloxytrimethoxysilane; A2, adding 3-chloropropylallyloxytrimethoxysilane and epichlorohydrin to ethylene glycol dimethyl ether, adding triethylamine dropwise at 0-5℃, heating to 80-90℃ for reaction, filtering after the reaction is completed, and distilling under reduced pressure.

[0007] In this invention, the preparation process of organosiloxanes containing epoxy-allyl bifunctional groups is divided into two steps, the core of which is the gradual introduction of the target functional group through nucleophilic substitution and condensation reactions. The first step uses 3-chloropropyltrimethoxysilane as the starting material, which undergoes a nucleophilic substitution reaction with allyl alcohol in anhydrous tetrahydrofuran. The silicon atom in the 3-chloropropyltrimethoxysilane molecule, due to its attachment to three methoxy groups and one chloropropyl group, possesses a partial positive charge and exhibits strong electrophilicity; the hydroxyl oxygen atom in the allyl alcohol molecule, due to its enrichment of lone pair electrons, exhibits strong nucleophilicity. Under the catalysis of sodium hydroxide, the hydroxyl oxygen of the allyl alcohol attacks the electron-deficient site of the silicon atom, and the chlorine atom is substituted as a leaving group, generating the intermediate product 3-chloropropylallyloxytrimethoxysilane. During the reaction, a water separator promptly removes the generated water, shifting the equilibrium towards the product and improving the reaction conversion rate. The key to this step lies in introducing the allyl group into the organosiloxane molecule through a nucleophilic substitution reaction, laying the foundation for the subsequent grafting reaction with the polyolefin substrate. In the second step, the intermediate 3-chloropropylallyloxytrimethoxysilane reacts further with epichlorohydrin in an ethylene glycol dimethyl ether system. The epoxy group (three-membered ring ether structure) in the epichlorohydrin molecule has high reactivity; its ring strain causes the oxygen atom of the epoxy group to attack the terminal chlorine atom of the chloropropyl group in the intermediate molecule, forming a new carbon-oxygen bond. Simultaneously, triethylamine acts as an acid-binding agent, binding with the hydrogen chloride generated in the reaction to prevent its inhibition of the reaction system. Heating to 80-90℃ accelerates the ring-opening reaction of the epoxy group. Finally, byproducts and solvents are removed by filtration and vacuum distillation to obtain an organosiloxane containing an epoxy-allyl bifunctional group. This step, by introducing the epoxy group, provides reaction sites for the sealing of hydroxyl groups on the surface of ceramic particles, while retaining the grafting activity of the allyl group, achieving a dual-functional design of "polarity regulation-interfacial grafting".

[0008] According to a preferred embodiment of the present invention, the ceramic particles were purchased from Jiangsu Hehai Nanotechnology Co., Ltd. (model: HH-Al2O3-1μm).

[0009] According to a preferred embodiment of the present invention, the 3-chloropropyltrimethoxysilane was purchased from Hubei Xingfa Chemical Group Co., Ltd. (model: XJ-3CP).

[0010] According to a preferred embodiment of the present invention, the allyl alcohol was purchased from Jiangsu Yida Chemical Co., Ltd. (model: YD-allyl-alcohol).

[0011] According to a preferred embodiment of the present invention, the tetrahydrofuran was purchased from Jiangsu Hualun Chemical Co., Ltd. (model: Hualun-THF-99.9%).

[0012] According to a preferred embodiment of the present invention, the nitrogen gas was purchased from Hangzhou Hangyang Co., Ltd. (model: HANGGAS-N2-99.999%).

[0013] According to a preferred embodiment of the present invention, the sodium hydroxide was purchased from Jiangsu Suhua Group (model: SuHua-NaOH-analytical grade).

[0014] According to a preferred embodiment of the present invention, the epichlorohydrin was purchased from Jiangsu Yangnong Chemical Group Co., Ltd. (model: YANGNONG-ECH-99.5%).

[0015] According to a preferred embodiment of the present invention, the ethylene glycol dimethyl ether was purchased from Jiangsu Hualun Chemical Co., Ltd. (model: Hualun-DME-99.9%).

[0016] According to a preferred embodiment of the present invention, the triethylamine was purchased from Jiangsu Feixiang Chemical Co., Ltd. (model: FX-Triethylamine-99%).

[0017] According to a preferred embodiment of the present invention, the dispersant was purchased from Jiangsu Hehai Nanotechnology Co., Ltd. (model: HH-PAA-20%).

[0018] According to a preferred embodiment of the present invention, the adhesive was purchased from Qilu Petrochemical Company (model: QL-SBR-1502).

[0019] According to a preferred embodiment of the present invention, the solvent was purchased from Jiangsu Runfeng Synthetic Technology Co., Ltd. (model: Runfeng-NMP-99.5%).

[0020] According to a preferred embodiment of the present invention, in step A1, the molar ratio of 3-chloropropyltrimethoxysilane to allyl alcohol is 1:1.2; the reaction time is 4-6 hours after heating to 60-70°C.

[0021] According to a preferred embodiment of the present invention, in step A2, the reaction time is 8-10 hours after heating to 80-90°C.

[0022] According to a preferred embodiment of the present invention, the method for preparing the organosiloxane containing isocyanate-amino bifunctional groups includes: B1, adding γ-aminopropyltrimethoxysilane and isophorone diisocyanate to N,N-dimethylformamide and stirring evenly under nitrogen protection; adding dibutyltin dilaurate and reacting at 70-80°C; B2, after the reaction is completed, distilling under reduced pressure to obtain N-(trimethoxysilylpropyl)isocyanate; adding N-(trimethoxysilylpropyl)isocyanate and ethylenediamine to ethanol and stirring at 25-30°C; filtering and distilling under reduced pressure after the reaction is completed. In this invention, the preparation of organosiloxanes containing isocyanate-amino bifunctional groups is divided into two steps, the core of which is the construction of a bifunctional structure through the addition reaction of isocyanate groups with amino groups. The first step uses γ-aminopropyltrimethoxysilane as a starting material, which undergoes an addition reaction with isophorone diisocyanate in an N,N-dimethylformamide system. The primary amino group (-NH2) in the γ-aminopropyltrimethoxysilane molecule possesses a lone pair of electrons, exhibiting strong nucleophilicity; the isocyanate group (-N=C=O) in the isophorone diisocyanate molecule is easily attacked by nucleophiles due to the positive charge of the carbonyl carbon. Under the catalysis of dibutyltin dilaurate, the lone pair of electrons of the amino group attacks the carbonyl carbon of the isocyanate group, forming a transition intermediate, which then rearranges to form a urea bond (-NH-CO-NH-), yielding the intermediate product N-(trimethoxysilylpropyl)isocyanate. During the reaction, nitrogen protection prevents moisture from damaging the isocyanate groups (water reacts with isocyanate groups to generate urea byproducts), ensuring efficient reaction. This step, by introducing amino groups and retaining some isocyanate groups, provides dual active sites for subsequent reactions with ceramic particles and polyolefin substrates. In the second step, the intermediate N-(trimethoxysilylpropyl)isocyanate reacts further with ethylenediamine in an ethanol system. The primary amino group (-NH2) in the ethylenediamine molecule also exhibits nucleophilicity, attacking the remaining carbonyl carbon of the isocyanate group in the intermediate molecule, undergoing another addition reaction to form a urea bond. Finally, the target product is obtained through filtration and vacuum distillation. This step, by controlling the reaction conditions (mild environment of 25-30℃), avoids excessive reaction leading to molecular chain crosslinking, ensuring that the product retains appropriate amounts of isocyanate and amino groups, providing flexible functional group control space for the interface modification of ceramic slurries.

[0023] According to a preferred embodiment of the present invention, the γ-aminopropyltrimethoxysilane was purchased from Hubei Xingfa Chemical Group Co., Ltd. (model: XJ-APS-99%).

[0024] According to a preferred embodiment of the present invention, the isophorone diisocyanate was purchased from Wanhua Chemical Group Co., Ltd. (model: WANICE-IPDI-99%).

[0025] According to a preferred embodiment of the present invention, the N,N-dimethylformamide was purchased from Jiangsu Hualun Chemical Co., Ltd. (model: Hualun-DMF-99.9%).

[0026] According to a preferred embodiment of the present invention, the dibutyltin dilaurate was purchased from Jiangsu Feixiang Chemical Co., Ltd. (model: FX-DBTDL-95%).

[0027] According to a preferred embodiment of the present invention, the ethylenediamine was purchased from Jiangsu Suhua Group (model: SuHua-Ethylenediamine-analytical grade).

[0028] According to a preferred embodiment of the present invention, the ethanol was purchased from Jiangsu Runfeng Synthetic Technology Co., Ltd. (model: Runfeng-Ethanol-95%).

[0029] According to a preferred embodiment of the present invention, in step B1, the molar ratio of γ-aminopropyltrimethoxysilane to isophorone diisocyanate is 1:0.8; the reaction time is 6-8 hours after heating to 70-80°C.

[0030] According to a preferred embodiment of the present invention, in step B2, the stirring reaction time is 4-5 hours at 25-30°C.

[0031] The present invention also provides a method for preparing the ceramic slurry, comprising the following steps: S1. Add ceramic particles to a solvent and disperse them ultrasonically to obtain a ceramic particle dispersion. Add dispersant and binder to the dispersion in sequence and stir at low speed. Adjust the pH of the system to 8-9, add the binder, heat to 50-60℃, and stir at high speed. S2. After cooling to room temperature, add an organosiloxane containing isocyanate-amino bifunctional groups and continue stirring; finally, add the remaining solvent.

[0032] In this invention, the preparation process of the ceramic slurry involves the synergistic effect of two modified organosiloxanes with ceramic particles and a polyolefin substrate. The core of this process is to improve the overall performance of the slurry through surface modification and interfacial reactions. Firstly, the surface of ceramic particles is rich in polar hydroxyl groups (-OH), which have a strong affinity for water but poor interfacial compatibility with the hydrophobic polyolefin substrate. The epoxy group (-O-CH2-CH(O)CH2-) in the organosiloxane molecule containing an epoxy-allyl bifunctional group undergoes a ring-opening reaction under weakly alkaline conditions (pH=8-9), and condenses with the hydroxyl groups on the surface of the ceramic particles (-OH + -O- → -O- + H2O), generating a stable siloxane bond (-Si-O-Ceramic-). This seals the polar sites of the ceramic particles, reduces their surface energy, and decreases the tendency for particle aggregation. Simultaneously, the allyl group (-CH2-CH=CH2) in the organosiloxane molecule undergoes a free radical grafting reaction with the carbon-carbon double bond of the polyolefin substrate (such as polyethylene and polypropylene) under the action of a free radical initiator (such as ammonium persulfate), forming a covalent bond (-CH2-CH=CH2+-CH2-CH2-→-CH2-CH(CH2-CH2-)-), chemically binding the ceramic particles to the polyolefin substrate and significantly improving the interfacial adhesion. Secondly, the amino group (-NH2) in the organosiloxane molecule containing the isocyanate-amino bifunctional group further reacts with the incompletely sealed hydroxyl groups on the surface of the ceramic particles, generating an amino bond (-NH-Ceramic-) through a condensation reaction, enhancing the modification effect on the ceramic surface; the isocyanate group (-N=C=O) in its molecule undergoes an addition reaction with the active hydrogen on the surface of the polyolefin substrate (such as residual catalysts or hydroxyl groups introduced during processing), generating a urea bond (-NH-CO-NH-), forming a second chemical bond connection. The synergistic effect of the two modifiers transforms the interfacial bonding between ceramic particles and the polyolefin substrate from physical adsorption to multiple chemical bonds, significantly improving the peel strength of the ceramic layer. Furthermore, the organosiloxane layer (containing silanol groups after methoxyl hydrolysis) formed on the surface of the ceramic particles by the two modifiers works synergistically with the dispersant (polycarboxylate) to form a stable double-layer structure on the particle surface, enhancing the electrostatic repulsion between particles, inhibiting agglomeration, resulting in no significant sedimentation of the slurry after 48 hours of standing, and significantly improving the uniformity of the coating thickness during the coating process.

[0033] According to a preferred embodiment of the present invention, in step S1, the ultrasonic dispersion time is 30-60 min; the low-speed stirring speed is 300-400 rpm for 10-15 min; and the high-speed stirring speed is 800-900 rpm for 2-3 h.

[0034] According to a preferred embodiment of the present invention, in step S2, the stirring time is continued for 1-1.5 hours; the remaining solvent is added to adjust the solid content to 30-40 wt%.

[0035] The present invention also provides an application of the ceramic slurry described above or the ceramic slurry prepared by the preparation method described above in a battery separator.

[0036] The beneficial effects of this invention are as follows: This invention utilizes two novel modified organosiloxanes to synergistically act on the surface of ceramic particles, combined with a specific preparation process, significantly improving the overall performance of ceramic slurries. It exhibits significant advantages in interfacial adhesion, dispersion stability, and functional adaptability. Regarding improved interfacial adhesion, traditional ceramic slurries suffer from poor interfacial compatibility due to the large surface energy difference between the polar hydroxyl groups on the ceramic particle surface and the polyolefin substrate, leading to easy coating detachment and high interfacial impedance. In this invention, the organosiloxane containing epoxy-allyl bifunctional groups undergoes a condensation reaction with the hydroxyl groups on the ceramic surface via epoxy groups, effectively sealing polar sites. Simultaneously, under the action of the allyl groups, it undergoes a grafting reaction with the polyolefin substrate, forming chemical bonds. The organosiloxane containing isocyanate-amino bifunctional groups further reacts with the remaining hydroxyl groups via the amino group, and under the action of the isocyanate groups, forms a stable urea bond structure with the active hydrogen on the substrate surface. The synergistic effect of the two modifiers transforms the interfacial bonding between the ceramic layer and the polyolefin substrate from physical adsorption to chemical bonding, significantly improving the peel strength and effectively preventing the coating from peeling off due to weak interfacial bonding during use, thereby greatly improving the long-term reliability of the battery separator.

[0037] Regarding enhanced dispersion stability, ceramic particles are prone to agglomeration due to their high surface energy, and traditional dispersants are insufficient to effectively inhibit this agglomeration, leading to sedimentation and uneven coating after the slurry has settled. In this invention, the amino component of an organosiloxane containing isocyanate-amino bifunctional groups can adjust the slurry pH to a weakly alkaline environment, synergistically forming a more stable double-layer structure on the ceramic particle surface with polycarboxylate dispersants, thus enhancing the electrostatic repulsion between particles. Simultaneously, the organosiloxane layer formed on the ceramic surface by the two modifiers reduces the particle surface energy, decreasing the tendency to agglomerate. Experiments show that the ceramic slurry exhibits no significant sedimentation after 48 hours of settling, and the coating thickness uniformity is significantly improved during the coating process, effectively avoiding local defects caused by uneven dispersion and ensuring the consistency of the battery separator.

[0038] Regarding functional adaptability optimization, traditional ceramic-coated separators suffer from problems such as high heat shrinkage and insufficient electrolyte wettability. In this invention, organosiloxanes containing epoxy-allyl bifunctional groups reduce sintering shrinkage between particles at high temperatures by sealing the hydroxyl groups on the ceramic surface; the amino component of organosiloxanes containing isocyanate-amino bifunctional groups enhances the hydrophilicity of the ceramic surface, and, in conjunction with the silanol groups generated by the hydrolysis of epoxy groups, significantly reduces the contact angle of the ceramic layer with the electrolyte, resulting in a significant increase in electrolyte absorption. These two improvements simultaneously enhance the dimensional stability of the battery separator at high temperatures and its ability to retain electrolyte, effectively reducing the safety risks of the battery under extreme conditions such as overcharging and short circuits, while also extending its cycle life.

[0039] In summary, this invention solves the problems of weak interfacial bonding, uneven dispersion, and insufficient functional adaptability of traditional ceramic slurries through the synergistic design and process optimization of dual modifiers. It provides key technical support for the preparation of high-performance lithium-ion battery separators and has important application value in improving battery safety, cycle life, and overall performance. Detailed Implementation

[0040] The following detailed embodiments are only used to further illustrate this application and should not be construed as limiting the scope of protection of this application. Those skilled in the art can make some non-essential improvements and adjustments to this application based on the above application content.

[0041] Example 1 Preparation of organosiloxanes containing epoxy-allyl bifunctional groups (modifier A, the same below): 100g of 3-chloropropyltrimethoxysilane and 33.6g of allyl alcohol were added to 500g of anhydrous tetrahydrofuran and stirred for 15min under nitrogen protection until homogeneous; 6g of sodium hydroxide was added as a catalyst, and the temperature was raised to 65℃ and kept constant for 5h. During the reaction, the generated water was continuously removed by a water separator; after the reaction was completed, tetrahydrofuran and unreacted allyl alcohol were removed by vacuum distillation to obtain 120g of the intermediate product 3-chloropropylallyloxytrimethoxysilane. 120g of intermediate 3-chloropropylallyloxytrimethoxysilane and 35g of epichlorohydrin were added to 300g of ethylene glycol dimethyl ether. 18g of triethylamine was slowly added dropwise at 3°C. After the addition was complete, the temperature was raised to 85°C and the reaction was carried out at a constant temperature for 9 hours. After the reaction was completed, the triethylamine hydrochloride precipitate was removed by filtration, and the target product, an organosiloxane containing an epoxy-allyl bifunctional group, was obtained by vacuum distillation.

[0042] Preparation of organosiloxanes containing isocyanate-amino bifunctional groups (modifier B, hereinafter the same): 120g of γ-aminopropyltrimethoxysilane and 192g of isophorone diisocyanate were added to 400g of N,N-dimethylformamide and stirred for 20min under nitrogen protection until homogeneous. 0.8g of dibutyltin dilaurate was added as a catalyst, and the mixture was heated to 75℃ and reacted at a constant temperature for 7h. After the reaction, N,N-dimethylformamide and excess isophorone diisocyanate were removed by vacuum distillation to obtain 70g of the intermediate product N-(trimethoxysilylpropyl)isocyanate. 70g of the intermediate N-(trimethoxysilylpropyl)isocyanate and 25g of ethylenediamine were added to 200g of ethanol and stirred at 28℃ for 4.5h. After the reaction, the ethanol was removed by filtration, and the target product, organosiloxane containing isocyanate-amino bifunctional groups, was obtained by vacuum distillation.

[0043] Preparation of ceramic slurry: 600g of ceramic particles were added to 20g of deionized water and ultrasonically dispersed at 200W for 40min to obtain a ceramic particle dispersion with a solid content of approximately 60wt%. 20g of polycarboxylate dispersant and 50g of styrene-butadiene rubber binder were added sequentially to the dispersion, and the mixture was stirred at 350rpm for 12min to ensure uniform coating of the ceramic particles by the dispersant and binder. The pH of the system was adjusted to 8.5 with ammonia, and 100g of an organosiloxane containing an epoxy-allyl bifunctional group was added. The mixture was heated to 55°C and stirred at 850 rpm for 2.5 h to allow modifier A to undergo the first surface modification through the condensation reaction of epoxy groups with hydroxyl groups on the surface of ceramic particles. After cooling to room temperature, 50 g of organosiloxane containing isocyanate-amino bifunctional groups was added, and stirring was continued at 850 rpm for 1.2 h to allow modifier B to react with the remaining hydroxyl groups through the amino groups and introduce isocyanate groups onto the surface of ceramic particles. Finally, the remaining deionized water was added to adjust the solid content to 35% to obtain the ceramic slurry for the battery separator.

[0044] Example 2 The specific implementation method is the same as in Example 1, except that the preparation of the organosiloxane containing the epoxy-allyl bifunctional group is as follows: 100g of 3-chloropropyltrimethoxysilane and 33.6g of allyl alcohol are added to 500g of anhydrous tetrahydrofuran and stirred evenly under nitrogen protection; 6g of sodium hydroxide is added, and the temperature is raised to 62℃ for 4h. During the reaction, the generated water is removed through a water separator; after the reaction, tetrahydrofuran and unreacted allyl alcohol are removed by vacuum distillation to obtain the intermediate product 3-chloropropylallyloxytrimethoxysilane. 120g of the intermediate 3-chloropropylallyloxytrimethoxysilane and 35g of epichlorohydrin are added to 300g of ethylene glycol dimethyl ether, and 18g of triethylamine is slowly added dropwise at 2℃. The temperature is raised to 90℃ for 10h. After the reaction, the triethylamine hydrochloride precipitate is removed by filtration, and the target product, the organosiloxane containing the epoxy-allyl bifunctional group, is obtained by vacuum distillation.

[0045] Preparation of organosiloxanes containing isocyanate-amino bifunctional groups: 120g of γ-aminopropyltrimethoxysilane and 192g of isophorone diisocyanate were added to 400g of N,N-dimethylformamide and stirred until homogeneous under nitrogen protection. 0.8g of dibutyltin dilaurate was added, and the mixture was heated to 70℃ and reacted for 8h. After the reaction, N,N-dimethylformamide and excess isophorone diisocyanate were removed by vacuum distillation to obtain 70g of the intermediate N-(trimethoxysilylpropyl)isocyanate. 70g of the intermediate N-(trimethoxysilylpropyl)isocyanate and 25g of ethylenediamine were added to 200g of ethanol and stirred at 30℃ for 5h. After the reaction, the ethanol was removed by filtration, and the target product, an organosiloxane containing isocyanate-amino bifunctional groups, was obtained by vacuum distillation.

[0046] Preparation of ceramic slurry: 700g of ceramic particles were added to 20g of N-methylpyrrolidone solvent and ultrasonically dispersed for 40min (power 200W) to obtain a ceramic particle dispersion (solid content approximately 60wt%). 20g of polycarboxylate dispersant and 50g of acrylate binder were added sequentially to the dispersion, and the mixture was stirred at 350rpm for 12min to ensure uniform coating of the ceramic particles by the dispersant and binder. The pH of the system was adjusted to 9 with ammonia, and 100g of an organosiloxane containing an epoxy-allyl bifunctional group was added. The mixture was heated to 55°C and stirred at 850 rpm for 2.5 h to allow modifier A to complete the first surface modification through the condensation reaction of epoxy groups with hydroxyl groups on the surface of ceramic particles. After cooling to room temperature, 50 g of organosiloxane containing isocyanate-amino bifunctional groups was added, and stirring was continued at 850 rpm for 1.2 h to allow modifier B to react with the remaining hydroxyl groups through amino groups and introduce isocyanate groups onto the surface of ceramic particles. Finally, the remaining N-methylpyrrolidone was added to adjust the solid content to 35% to obtain the ceramic slurry for battery separators.

[0047] Example 3 The specific implementation method is the same as in Example 1, except that the preparation of the organosiloxane containing epoxy-allyl bifunctional groups is as follows: 100g of 3-chloropropyltrimethoxysilane and 33.6g of allyl alcohol are added to 500g of anhydrous tetrahydrofuran and stirred evenly under nitrogen protection; 6g of sodium hydroxide is added, and the temperature is raised to 65℃ for 5h. During the reaction, the generated water is removed through a water separator; after the reaction, tetrahydrofuran and unreacted allyl alcohol are removed by vacuum distillation to obtain 120g of the intermediate product 3-chloropropylallyloxytrimethoxysilane. 120g of the intermediate 3-chloropropylallyloxytrimethoxysilane and 35g of epichlorohydrin are added to 300g of ethylene glycol dimethyl ether, and 18g of triethylamine is slowly added dropwise at 5℃. The temperature is raised to 85℃ for 9h. After the reaction, the triethylamine hydrochloride precipitate is removed by filtration, and the target product, the organosiloxane containing epoxy-allyl bifunctional groups, is obtained by vacuum distillation.

[0048] Preparation of organosiloxanes containing isocyanate-amino bifunctional groups: 120g of γ-aminopropyltrimethoxysilane and 192g of isophorone diisocyanate were added to 400g of N,N-dimethylformamide and stirred until homogeneous under nitrogen protection. 0.8g of dibutyltin dilaurate was added, and the mixture was heated to 75℃ and reacted for 7h. After the reaction, N,N-dimethylformamide and excess isophorone diisocyanate were removed by vacuum distillation to obtain 70g of the intermediate N-(trimethoxysilylpropyl)isocyanate. 70g of the intermediate N-(trimethoxysilylpropyl)isocyanate and 25g of ethylenediamine were added to 200g of ethanol and stirred at 28℃ for 4.5h. After the reaction, the ethanol was removed by filtration, and the target product, an organosiloxane containing isocyanate-amino bifunctional groups, was obtained by vacuum distillation.

[0049] Preparation of ceramic slurry: 500g of ceramic particles were added to 20g of deionized water and ultrasonically dispersed for 40min (power 200W) to obtain a ceramic particle dispersion (solid content approximately 60wt%). 20g of polycarboxylate dispersant and 50g of styrene-butadiene rubber binder were added sequentially to the dispersion, and the mixture was stirred at 350rpm for 12min to ensure uniform coating of the ceramic particles by the dispersant and binder. The pH of the system was adjusted to 8.1 with ammonia, and 100g of an organosiloxane containing an epoxy-allyl bifunctional group was added. g, heated to 55℃, and stirred at 850 rpm for 2.5 h to allow modifier A to complete the first surface modification through the condensation reaction of epoxy groups with hydroxyl groups on the surface of ceramic particles; after cooling to room temperature, 50 g of organosiloxane containing isocyanate-amino bifunctional groups was added, and stirring was continued at 850 rpm for 1.2 h to allow modifier B to react with the remaining hydroxyl groups through amino groups and introduce isocyanate groups on the surface of ceramic particles; finally, the remaining deionized water was added to adjust the solid content to 35% to obtain the ceramic slurry for battery separator.

[0050] Comparative Example 1 The specific implementation method is the same as in Example 1, except that the ceramic slurry is prepared as follows: 600g of ceramic particles are added to 20g of deionized water and ultrasonically dispersed for 40min (power 200W) to obtain a ceramic particle dispersion (solid content approximately 60wt%); 20g of dispersant polycarboxylate and 50g of binder styrene-butadiene rubber are added to the dispersion in sequence, and the mixture is stirred at a low speed of 350rpm for 12min to ensure that the dispersant and binder uniformly coat the ceramic particles; the pH of the system is adjusted to 8.5 with ammonia, and 50g of organosiloxane containing isocyanate-amino bifunctional groups is added. The mixture is heated to 55℃ and stirred at a high speed of 850rpm for 2.5h to allow the modifier B to react with the hydroxyl groups on the surface of the ceramic particles through the amino group; after cooling to room temperature, stirring is continued at 850rpm for 1.2h; finally, the remaining deionized water is added to adjust the solid content to 35% to obtain the ceramic slurry.

[0051] Comparative Example 2 The specific implementation method is the same as in Example 1, except that the ceramic slurry is prepared as follows: 600g of ceramic particles are added to 20g of deionized water and ultrasonically dispersed for 40min (power 200W) to obtain a ceramic particle dispersion (solid content of about 60wt%); 20g of dispersant polycarboxylate and 50g of binder styrene-butadiene rubber are added to the dispersion in sequence, and the mixture is stirred at a low speed of 350rpm for 12min to ensure that the dispersant and binder uniformly coat the ceramic particles; the pH of the system is adjusted to 8.5 with ammonia water, and 100g of organosiloxane containing epoxy-allyl bifunctional groups is added. The temperature is raised to 55℃ and stirred at a high speed of 850rpm for 2.5h to allow the modifier A to undergo a condensation reaction with the hydroxyl groups on the surface of the ceramic particles through epoxy groups; after cooling to room temperature, the remaining deionized water is added to adjust the solid content to 35% to obtain the ceramic slurry.

[0052] Comparative Example 3 The specific implementation method is the same as in Example 1, except that the ceramic slurry is prepared as follows: 600g of ceramic particles are added to 20g of deionized water and ultrasonically dispersed for 40min (power 200W) to obtain a ceramic particle dispersion (solid content of about 60wt%); 20g of dispersant polycarboxylate and 50g of binder styrene-butadiene rubber are added to the dispersion in sequence, and the mixture is stirred at a low speed of 350rpm for 12min to ensure that the dispersant and binder uniformly coat the ceramic particles; the pH of the system is adjusted to 8.5 with ammonia water, 100g of traditional silane coupling agent KH550 (γ-aminopropyltriethoxysilane) is added, the temperature is raised to 55℃, and the mixture is stirred at a high speed of 850rpm for 2.5h; after cooling to room temperature, the remaining deionized water is added to adjust the solid content to 35% to obtain the ceramic slurry.

[0053] Performance testing The ceramic slurries prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests according to the following methods: 1. Interfacial Adhesion (Peel Strength) Test: Ceramic slurry was coated onto the surface of a polyethylene (PE) substrate (12μm thick) using a microgravure coating machine. The coating thickness was controlled at 3-5μm, and the coating was dried at 60℃ for 3 minutes to form a ceramic-coated diaphragm. The coated diaphragm was cut into strips of 100mm × 25mm and bonded to another uncoated PE substrate of the same size (as a backing) with double-sided adhesive to form a "ceramic coating-PE-PE" sandwich structure. The peel strength was tested using a universal testing machine (tensile rate 10mm / min), and the maximum force required to completely peel the ceramic coating from the PE substrate was recorded (unit: N / m).

[0054] 2. Dispersion stability test: Pour 50g of ceramic slurry into a 100mL transparent glass test tube, seal it, and place it in a 25℃ constant temperature oven for 48 hours. Observe and record whether there is obvious sedimentation and stratification. At the same time, use a laser particle size analyzer (Malvern Zetasizer Nano ZS) to measure the Zeta potential of ceramic particles in the slurry (temperature 25℃, equilibrium time 120 seconds) and calculate its absolute value.

[0055] 3. Heat shrinkage resistance test: Cut the coated ceramic membrane (thickness 3-5μm) into 50mm×50mm squares, fix them in the heat shrinkage tester (ETR-100), heat them at a constant temperature of 120℃ for 1 hour, and after cooling to room temperature, measure the longitudinal and transverse dimensional change rates (shrinkage rate = (original size - heated size) / original size × 100%), and take the average of the longitudinal and transverse shrinkage rates as the final result.

[0056] 4. Electrolyte wettability test: Cut the ceramic slurry-coated diaphragm (after drying) into 20mm × 20mm squares. Rinse the surface three times with deionized water to remove uncured components, and place it in an environment of 25℃ and 50% relative humidity for 24 hours to equilibrate. Use a contact angle meter (Krüss DSA25) to measure the contact angle between the diaphragm surface and the electrolyte (ethylene carbonate: dimethyl carbonate: lithium carbonate = 1:1:0.1, mass ratio) (contact time 10 seconds, droplet volume 5μL); at the same time, immerse the diaphragm in the electrolyte, time for 1 minute, remove it, absorb excess electrolyte on the surface with filter paper, weigh it and calculate the absorbed amount (absorbed amount = (mass after immersion - mass before immersion) / mass before immersion × 100%).

[0057] 5. Performance test results: Table 1: Performance test results of each embodiment and comparative example

[0058] As can be seen from Table 1, Examples 1-3 systematically solved the four major technical problems of existing ceramic slurries through the synergistic effect of two newly designed modified organosiloxanes (containing epoxy-allyl bifunctional groups and isocyanate-amino bifunctional groups): In terms of interfacial bonding, traditional ceramic slurries rely solely on physical adsorption to bond due to the large difference in surface energy between the hydroxyl groups on the surface of ceramic particles and the polyolefin substrate, resulting in low peel strength (0.6-1.5 N / m in Comparative Examples 1-3). In Examples 1-3, modifier A, containing epoxy-allyl bifunctional groups, seals polar sites through the condensation reaction of epoxy groups with hydroxyl groups on the ceramic surface, while the allyl groups undergo free radical grafting reactions with the polyolefin substrate to form covalent bonds. Modifier B, containing isocyanate-amino bifunctional groups, reacts with the remaining hydroxyl groups through the reaction of amino groups, forming urea bonds between the isocyanate groups and the active hydrogens of the substrate. This dual chemical bonding transforms the interfacial bonding from physical adsorption to multiple chemical bond connections, ultimately increasing the peel strength to 2.1-2.3 N / m (Examples 1-3), significantly better than the comparative examples. Regarding dispersion stability, traditional ceramic particles are prone to agglomeration due to their high surface energy, and the slurry tends to settle after standing (comparative examples 1-3 showed slight to severe sedimentation, with absolute Zeta potential values ​​of only -20 to -35 mV). In the examples, the amino component of modifier B adjusts the pH of the slurry to weakly alkaline (8.1-9), and together with the polycarboxylate dispersant, forms a stable electric double layer on the surface of ceramic particles, enhancing the electrostatic repulsion between particles; at the same time, the organosiloxane layer formed on the particle surface by the two modifiers reduces the surface energy and inhibits the tendency to agglomerate. Finally, the slurry showed no obvious sedimentation after 48 hours, and the absolute value of the Zeta potential increased to -46~-48mV (Examples 1-3), and the dispersion stability was significantly improved.

[0059] Regarding heat shrinkage resistance, traditional ceramic coatings, due to the lack of sealing of surface hydroxyl groups, are prone to sintering shrinkage between particles at high temperatures (comparative Examples 1-3, shrinkage rate 4.8%-7.5%). In the examples, the epoxy groups of modifier A sealed most of the polar sites through a condensation reaction with the hydroxyl groups on the ceramic surface, reducing the dehydration condensation reaction between hydroxyl groups at high temperatures, thereby inhibiting sintering shrinkage between particles. Ultimately, the thermal shrinkage rate of the ceramic layer decreased to 2.8%-3.1% (Examples 1-3), far lower than the comparative examples. Regarding electrolyte wettability, traditional ceramic surfaces, due to the strong polarity of hydroxyl groups but insufficient affinity for electrolytes, exhibit large contact angles and low liquid absorption (comparative Examples 1-3, contact angle 38-45°, liquid absorption 95%-125%). In the examples, the epoxy groups of modifier A hydrolyze to generate silanol groups, and the amino groups of modifier B enhance the surface hydrophilicity. The two work synergistically to improve the wetting ability of the ceramic surface to the electrolyte, reducing the contact angle to 22-24° and increasing the electrolyte absorption rate to 158%-165% per minute (Examples 1-3), effectively enhancing the electrolyte retention capacity. In summary, Examples 1-3, through the synergistic effect of the two modifiers—"surface hydroxyl group blocking - polymer interface grafting - improved dispersion stability - enhanced hydrophilicity"—comprehensively solve the technical defects of traditional ceramic slurries, providing key technical support for the preparation of high-performance lithium-ion battery ceramic coated separators.

[0060] The above-described embodiments are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A ceramic slurry, characterized by, The raw materials include the following weight parts: ceramic particles: 500-800 parts by weight; an organosiloxane containing epoxy-allyl bifunctional groups: 50-150 parts by weight; an organosiloxane containing isocyanate-amino bifunctional groups: 30-100 parts by weight; a dispersant: 10-50 parts by weight; a binder: 20-80 parts by weight; a solvent: 10-30 parts by weight; The preparation method of the organosiloxane containing epoxy-allyl bifunctional groups includes: A1, adding 3-chloropropyltrimethoxysilane and allyl alcohol into anhydrous tetrahydrofuran, stirring uniformly under nitrogen protection; adding sodium hydroxide, and reacting at 60-70°C; removing the generated water through a water trap during the reaction; after the reaction, performing reduced pressure distillation to obtain 3-chloropropylallyloxytrimethoxysilane; A2, adding 3-chloropropylallyloxytrimethoxysilane and epichlorohydrin into ethylene glycol dimethyl ether, adding triethylamine dropwise at 0-5°C, and reacting at 80-90°C; after the reaction, performing filtration and reduced pressure distillation.

2. The ceramic slurry of claim 1, wherein, In step A1, the molar ratio of 3-chloropropyltrimethoxysilane to allyl alcohol is 1:1.2; the reaction time at 60-70°C is 4-6h.

3. The ceramic slurry of claim 1, wherein, In step A2, the reaction time at 80-90°C is 8-10h.

4. The ceramic slurry of claim 1, wherein, The preparation method of the organosiloxane containing isocyanate-amino bifunctional groups includes: B1, adding γ-aminopropyltrimethoxysilane and isophorone diisocyanate into N,N-dimethylformamide, stirring uniformly under nitrogen protection; adding dibutyltin dilaurate, and reacting at 70-80°C; B2, after the reaction, performing reduced pressure distillation to obtain N-(trimethoxysilylpropyl) isocyanate; adding N-(trimethoxysilylpropyl) isocyanate and ethylenediamine into ethanol, and stirring and reacting at 25-30°C; after the reaction, performing filtration and reduced pressure distillation.

5. The ceramic slurry of claim 4, wherein, In step B1, the molar ratio of γ-aminopropyltrimethoxysilane to isophorone diisocyanate is 1:0.8; the reaction time at 70-80°C is 6-8h.

6. The ceramic slurry of claim 4, wherein, In step B2, the stirring and reacting time at 25-30°C is 4-5h.

7. A method for the preparation of a ceramic slurry according to any one of claims 1-6, characterized by the steps of It includes: S1, adding ceramic particles into a solvent, ultrasonic dispersion to obtain a ceramic particle dispersion liquid; sequentially adding a dispersant and a binder into the dispersion liquid, and stirring at a low speed; adjusting the pH of the system to 8-9, adding a solvent, and stirring at a high speed after heating to 50-60°C; S2, after cooling to room temperature, adding an organosiloxane containing isocyanate-amino bifunctional groups, and continuing to stir; finally adding the remaining solvent.

8. The preparation method according to claim 7, characterized in that, In step S1, the ultrasonic dispersion time is 30-60min; the stirring speed at a low speed is 300-400rpm, and the time is 10-15min; the stirring speed at a high speed is 800-900rpm, and the time is 2-3h.

9. The preparation method according to claim 7, characterized in that, In step S2, the continuing stirring time is 1-1.5h; the remaining solvent is added to adjust the solid content to 30-40wt%.

10. Use of a ceramic slurry according to any one of claims 1 to 6 or a ceramic slurry prepared according to the method of any one of claims 7 to 9, characterized in that, The application of the ceramic slurry in a battery separator.

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