Thermally conductive flame-retardant sealant for power batteries and preparation method thereof

Abstract

The present application belongs to the field of sealant technology, and specifically relates to a heat-conducting flame-retardant sealant for power batteries and its preparation method. By collaboratively designing a composite heat-conducting filler with a polyglutamic acid-melamine cyanurate-calcium hydrogen phosphate composite flame retardant, combined with magnetic field dispersion, ultrasonic blending and silane coupling agent interface optimization technology, the thermal conductivity and flame retardancy of the material are significantly improved. The lithium silicate glass ceramic precursor is surface-modified by phosphorus oxychloride to enhance the bonding between the filler and the matrix. The amino-terminated polyether and the isocyanate curing agent construct a flexible cross-linked network to ensure mechanical strength and thermal stability. The sealant suppresses the propagation of combustion through a multi-stage reaction mechanism in the event of thermal runaway, reduces the release of toxic gases, and adapts to the high-frequency vibration and thermal cycling conditions of the battery module. The preparation process achieves a synergistic enhancement of thermal conductivity and flame retardancy through gradient stirring, vacuum degassing and uniform dispersion of fillers.

Description

Technical Field

[0001] The present application belongs to the technical field of sealants, and specifically relates to a thermally conductive flame-retardant sealant for power batteries and a preparation method thereof. Background Art

[0002] As a core component of new energy vehicles, the performance of power batteries is directly related to the safety, endurance, and service life of the entire vehicle. With the rapid development of new energy vehicle technology, the trend towards integrated power batteries and higher energy density is becoming increasingly prominent. In particular, with the application of new battery structures such as CTP and blade battery technology, battery module design places higher demands on the comprehensive performance of materials. Among them, sealants, as functional materials in power battery modules, fulfill multiple functions, including structural bonding and environmental sealing.

[0003] Early power battery module designs often used materials such as epoxy resin potting compounds and polyurethane potting compounds. While these materials possess certain bonding strength and insulation properties, they lack significant advantages in thermal conductivity, flame retardancy, and long-term service stability. Epoxy resin potting compounds have a high shrinkage rate during curing, which can easily lead to microcracks at the interfaces between battery cells, thereby affecting heat dissipation. While polyurethane potting compounds offer good flexibility, their thermal conductivity is generally low, typically below 1W / m·K, making them incapable of meeting the rapid heat dissipation requirements of high-power battery modules. Furthermore, traditional materials are prone to thermal decomposition at high temperatures, releasing toxic gases and posing safety risks. To address these issues, the industry has gradually introduced new materials such as silicone-based thermally conductive adhesives and modified silane sealants in recent years. For example, silicone potting compounds offer excellent high and low temperature resistance and elasticity. Their thermal conductivity can be increased to 1-3W / m·K by adding highly conductive fillers such as aluminum nitride, boron nitride, and zinc oxide. Some high-end products can even reach 4-5W / m·K. However, this type of material still has limitations in terms of flame retardancy, especially in thermal runaway scenarios caused by high temperature or short circuit. The flame retardancy of silicone materials depends on the type and ratio of fillers, and after long-term service, the performance is easily degraded due to filler sedimentation or interface failure. In addition, the bonding strength of silicone materials is relatively low, which makes it difficult to meet the high-strength bonding requirements between battery cells and structural components in CTP battery packs. In terms of flame retardancy, existing technologies mainly achieve this by adding inorganic flame retardants such as aluminum hydroxide and magnesium hydroxide. These flame retardants delay the combustion of the material through the mechanism of dehydration and heat absorption, but their addition amount usually needs to reach more than 30% to meet the flame retardancy standards. However, a high proportion of inorganic flame retardants will significantly increase the viscosity of the material, reduce its fluidity and processing performance, and lead to problems such as uneven filling and residual bubbles during the potting process. At the same time, the long-term thermal stability of flame retardants is poor, and they are prone to migration or agglomeration under the high-frequency vibration and thermal cycling conditions of the battery module, thereby weakening the flame retardant effect.

[0004] In summary, while the thermal conductivity and flame retardancy of existing sealants can be improved through filler optimization, the addition of fillers often comes at the expense of the material's mechanical properties. The addition of highly thermally conductive fillers or flame retardants significantly increases the material's rigidity, leading to a significant decrease in elongation at break, making it susceptible to brittle fracture when the battery module is subjected to impact or vibration. Furthermore, the impact of filler particle size distribution and interfacial bonding on thermal conductivity has yet to be fully resolved. Single-particle fillers have difficulty forming continuous thermal conduction channels within the matrix, and while multi-grade particle size combinations can improve thermal conductivity, they can easily cause filler sedimentation, resulting in uneven thermal conductivity and even localized overheating. Summary of the Invention

[0005] In order to solve the shortcomings of existing sealants for power batteries in terms of thermal conductivity, flame retardancy, mechanical properties, environmental adaptability and long-term service reliability.

[0006] The present application provides a thermally conductive flame-retardant sealant for a power battery, comprising the following components:

[0007] 15-30 parts of amino-terminated polyether, 8-18 parts of lithium silicate glass ceramic precursor, 12-22 parts of polyglutamic acid-melamine cyanurate-calcium hydrogen phosphate composite flame retardant, 40-55 parts of composite thermal conductive filler, 2-4 parts of silane coupling agent, 5-9 parts of isocyanate curing agent;

[0008] The composite thermally conductive filler comprises:

[0009] 27-35 parts of modified aluminum nitride fiber, 10-15 parts of mica powder, and 3-5 parts of boron nitride nanotubes.

[0010] Furthermore, the lithium silicate glass ceramic precursor is lithium aluminum silicate glass powder, which also includes 5-8wt% ZnO.

[0011] Furthermore, the lithium aluminum silicate glass powder is reacted with phosphorus oxychloride at a mass ratio of 1.5-2.5:1 in a nitrogen atmosphere at 70-90° C. for 1-3 hours to graft -PO(OH)2 groups on the surface of the glass powder, and the reaction is followed by washing with water and drying.

[0012] Furthermore, the polyglutamic acid-melamine cyanurate-calcium hydrogen phosphate composite flame retardant is prepared by the following method:

[0013] A. co-precipitating γ-polyglutamic acid and melamine cyanurate at a mass ratio of 1.5-2.5:1 at a pH of 9-11 to form a polyglutamic acid-MCA core-shell structure;

[0014] B. The product obtained in step A is chelated with calcium hydrogen phosphate at a pH of 8-10 to form nanoparticles of 50-100 nm;

[0015] C. Add 5-10% magnesium ammonium phosphate to an electrolyte solution, and treat at 37°C for 12-36 hours to form a hydroxyapatite coating layer. The electrolyte solution contains 135-150 mmol / L NaCl, 4-6 mmol / L KCl, 2-3 mmol / L CaCl2, 0.8-1.2 mmol / L MgCl2·6H2O, 3.5-5 mmol / L NaHCO3, and 0.8-1.2 mmol / L KH2PO4, with a pH of 7.2-7.6.

[0016] Furthermore, the preparation method of the modified aluminum nitride fiber is as follows:

[0017] Aluminum nitride fibers were etched with a 1-5wt% NaOH solution to form nanogrooves with a depth of 20-50nm, then treated with a 1-3wt% KH-550 solution, and then treated in an electrolyte solution containing 0.3-0.7wt% PVA, wherein the electrolyte solution contained 135-150mmol / L NaCl, 4-6mmol / L KCl, 2-3mmol / L CaCl2, 0.8-1.2mmol / L MgCl2·6H2O, 3.5-5mmol / L NaHCO3, and 0.8-1.2mmol / L KH2PO4, with a pH of 7.2-7.6.

[0018] The present application also provides a method for preparing a thermally conductive flame-retardant sealant for a power battery, comprising the following steps:

[0019] S1. A molecular weight of 3000-5000 amino-terminated polyether is mixed with a lithium silicate glass ceramic precursor at 85-95 ° C, a silane coupling agent is added, and after the reaction is completed, a hydrogen bond network matrix is ​​obtained;

[0020] S2. The wet-ground phlogopite was added to a 2-5wt% KH-560 ethanol solution and stirred at 70-80 ° C for 1-2h. After washing and drying, the mica powder was mixed with a polyglutamic acid - melamine cyanurate - calcium hydrogen phosphate composite flame retardant in a mass ratio of 1:0.2-0.5 in deionized water and ultrasonically dispersed for 30-50min and dried for later use.

[0021] S3 disperses the modified aluminum nitride fiber and the product obtained in S2 in a 0.3-0.7T magnetic field, then adds boron nitride nanotubes and ultrasonically blends for 1-2 hours;

[0022] S4. Add the product obtained in S3 and the remaining polyglutamic acid-melamine cyanurate-calcium hydrogen phosphate composite flame retardant to the matrix obtained in S1, stir at 50-70°C for 20-40 minutes at a revolution of 100-200 rpm and a rotation of 1000-1500 rpm in a planetary mixer, heat to 85-95°C, stir at a revolution of 150-250 rpm and a rotation of 1500-2000 rpm for 0.5-1.5 hours, add isocyanate curing agent, and degas at a vacuum degree of -0.08-0.09 MPa for 15-30 minutes to prepare a sealant.

[0023] Furthermore, after adding the isocyanate curing agent in step S4, 2-3 parts of amino-terminated polyether with a molecular weight of 800-1200 are added.

[0024] Furthermore, after adding the silane coupling agent in step S1, 2-5 parts of TiO2 are added as a nanocrystal nucleating agent.

[0025] In this application, amino-terminated polyether is used as the base resin. Its molecular weight of 3,000-5,000 balances the material's flexibility and reactivity. The amino groups in its molecular chain can undergo a cross-linking reaction with the isocyanate curing agent to form a three-dimensional network structure, giving the sealant good elasticity and vibration resistance. In addition, the low glass transition temperature of amino-terminated polyether is typically below -50°C, which ensures that the sealant maintains flexibility over a wide temperature range of -40°C to 150°C, avoiding interfacial cracking caused by thermal expansion and contraction.

[0026] The lithium silicate glass ceramic precursor uses lithium aluminum silicate glass powder, which also contains 5-8wt% ZnO. The glass ceramic precursor in the sealant mainly plays the role of enhancing the thermal stability of the material and improving the high-temperature performance. The introduction of this material can enhance the long-term thermal stability of the sealant, so that it can still maintain structural integrity under the high-frequency vibration and thermal cycling conditions of the battery module. The addition of ZnO, on the one hand, can adjust the thermal expansion coefficient of the glass ceramic, so that it better matches other materials in the battery module, reduce the interfacial stress concentration caused by the large difference in thermal expansion coefficient, and thus improve the bonding strength and long-term stability between the sealant and the battery assembly; on the other hand, ZnO can also participate in the formation process of glass ceramics to a certain extent, optimize its microstructure, enhance the density of the glass ceramic phase, and further improve the overall performance of the material. The introduction of ZnO can reduce the softening temperature of the glass powder, promote the ceramicization process, and further inhibit combustion through synergistic action with flame retardants. Lithium silicate glass-ceramic precursors are made from lithium aluminosilicate glass powder surface-modified with phosphorus oxychloride. During the preparation process, the lithium aluminosilicate glass powder is mixed with phosphorus oxychloride and then reacted. The core of this treatment process is the chemical introduction of -PO(OH)2 groups onto the glass powder surface. Phosphorus oxychloride reacts with the hydroxyl groups on the glass powder surface to form phosphate ester structures, which can form hydrogen bonds with amino-terminated polyethers, thereby strengthening the interfacial bonding between the filler and the matrix. Furthermore, the introduction of -PO(OH)2 groups increases the material's hydrophilicity, making it easier to disperse in the sealant and reducing agglomeration. After washing and drying, the surface of the glass-ceramic precursor is more active, allowing it to further bond with silane coupling agents, thereby improving the overall performance of the material. At high temperatures, the lithium silicate glass-ceramic precursor undergoes a ceramic reaction, forming a dense ceramic layer that effectively blocks heat transfer and oxygen diffusion. The optimization of the lithium silicate glass-ceramic precursor is reflected not only in its thermal stability and interfacial bonding ability, but also in its contribution to the overall performance of the sealant. By adjusting the molar ratio of glass frit to phosphorus oxychloride, the density of -PO(OH)2 groups can be controlled, thereby affecting the bonding strength with the substrate. A high molar ratio may result in an excess of phosphate groups, which in turn reduces the stability of the material; while a low molar ratio may not be sufficient to form an effective interfacial bond.

[0027] The polyglutamic acid-melamine cyanurate-dicalcium phosphate composite flame retardant is prepared via a three-step process. γ-Polyglutamic acid is co-precipitated with melamine cyanurate (MCA) under alkaline conditions to form a core-shell structure. The key to this process lies in controlling the pH value. A higher pH promotes the deprotonation of polyglutamic acid, allowing it to interact with the ions of MCA, resulting in a stable core-shell structure. The advantage of this core-shell structure lies in its ability to delay combustion through both physical and chemical mechanisms. The polyglutamic acid polymer chains decompose through endothermic decomposition during the initial combustion phase, reducing the material's temperature rise rate. MCA decomposes at high temperatures to produce melamine and cyanuric acid, which further absorb heat and release inert gases, diluting the oxygen concentration and suppressing the combustion reaction. This core-shell design not only improves the flame retardant's dispersibility but also enhances its flame retardant effect through a multi-stage reaction mechanism. In step B, the polyglutamic acid-MCA core-shell structure chelates with dicalcium phosphate to form nanoparticles measuring 50-100 nm. The core of this process lies in the interaction between dicalcium phosphate and polyglutamic acid. The introduction of calcium hydrogen phosphate can undergo a chelating reaction with the carboxylic acid groups of polyglutamic acid to form a stable inorganic-organic complex. The formation of these nanoparticles not only increases the surface area of ​​the flame retardant, but also improves its dispersibility in the matrix due to its tiny particle size. During the combustion process, calcium hydrogen phosphate can decompose to form calcium oxide and calcium phosphate. These products have high thermal stability and can form a continuous inorganic protective layer at high temperatures, isolating the transfer of heat and oxygen, thereby delaying the combustion process. In addition, the uniform distribution of nanoparticles reduces local thermal resistance caused by filler aggregation, ensuring that the flame retardant exerts a consistent protective effect throughout the sealant. In step C, a hydroxyapatite coating is formed by adding 5-10% ammonium magnesium phosphate to the electrolyte solution for treatment. The purpose of this coating is to further enhance the thermal stability and interfacial bonding ability of the flame retardant. Hydroxyapatite is an inorganic material with excellent thermal stability and chemical inertness. Its coating can form a dense protective film at high temperatures, reducing the thermal decomposition rate of the material. Furthermore, the introduction of hydroxyapatite, through its high melting point, provides an additional thermal barrier in thermal runaway scenarios, thereby slowing the propagation of the combustion reaction. The formation of this coating not only improves the thermal stability of the flame retardant but also, through its interfacial bonding with the substrate, reduces performance degradation caused by interface weakening.

[0028] The composite thermally conductive filler consists of modified aluminum nitride fibers, mica powder, and boron nitride nanotubes. The aluminum nitride fibers are etched with a NaOH solution to form nanogrooves. The low NaOH concentration selectively etches the fiber surface, creating regular nanogrooves without disrupting the fiber's main structure. These grooves increase the fiber's surface area, enhancing its contact area with the matrix material and improving thermal conductivity. Furthermore, the nanogrooves serve as anchor points for the thermally conductive filler, physically embedding it to strengthen the interfacial bond between the fiber and the matrix. During the service life of the battery module, this modified design reduces heat accumulation caused by interfacial thermal resistance, thereby improving the material's thermal conductivity. The modified aluminum nitride fibers are treated with a KH-550 solution to strengthen the interfacial bond between the filler and the matrix through chemical bonding. The amino groups of the KH-550 on the aluminum nitride fiber surface react with the fiber's surface hydroxyl groups to form stable siloxane bonds. This chemical bond not only improves fiber dispersion but also mitigates the degradation of thermal conductivity caused by interfacial weakening. During the preparation of the sealant, aluminum nitride fibers treated with KH-550 can form a more uniform distribution in the matrix, thereby reducing filler agglomeration and further optimizing thermal conductivity. The modified aluminum nitride fibers are treated in an electrolyte solution containing PVA. The introduction of PVA can further improve the dispersion and interfacial bonding ability of the fibers through the flexibility of its molecular chains. The PVA molecular chains can combine with the hydroxyl groups on the fiber surface through hydrogen bonds to form a stable physical adsorption layer. This treatment method not only improves the dispersion of the fibers in the matrix, but also reduces the agglomeration between fibers through the bridging effect of the PVA molecular chains. In addition, the introduction of PVA can provide additional thermal stability to the fibers through its decomposition characteristics at high temperatures. During the use of the sealant, this modified design can ensure that the aluminum nitride fibers remain evenly distributed in the matrix, thereby maximizing thermal conductivity and reducing local thermal resistance caused by filler aggregation.

[0029] The primary function of silane coupling agents is to strengthen the interfacial bond between the filler and the matrix, mitigating performance degradation caused by interfacial weakening. They introduce reactive groups onto the filler surface, thereby improving filler dispersibility and stability. Isocyanate curing agents react with the amino groups of amino-terminated polyethers to form a cross-linked polyurethane network. This cross-linking structure not only enhances the sealant's mechanical strength and durability but also strengthens its resistance to thermal stress.

[0030] The synergistic effect of each component is the core of the sealant performance optimization described in this application. The mixture of terminal amino polyether and lithium silicate glass ceramic precursor provides good thermal stability and flexibility for the matrix, and the addition of composite flame retardant and thermal conductive filler improves the flame retardant and thermal conductivity respectively. The silane coupling agent reduces the problem of thermal conductivity degradation and flame retardant migration caused by interface weakening by reinforcing the interface between the filler and the matrix. The isocyanate curing agent improves the mechanical strength and durability of the material through cross-linking reaction. Through the processing of steps S1 to S4, the distribution of all components in the matrix is ​​more uniform, thereby achieving a synergistic enhancement of thermal conductivity and flame retardant properties. This design not only solves the shortcomings of traditional sealants in thermal conductivity and flame retardant properties, but also overcomes the problem of uneven performance caused by filler sedimentation and interface failure.

[0031] In the preparation process, the mica powder in step S2 is treated with a KH-560 ethanol solution, which can form a more stable interface bond with the matrix material, thereby improving the dispersibility and thermal conductivity of the mica powder. During the ultrasonic blending process, the polyglutamic acid-melamine cyanurate-calcium hydrogen phosphate composite flame retardant forms an interfacial chemical bond with the mica powder through mechanochemical action. The non-combustible gas produced by the decomposition of melamine cyanurate is physically intercepted by the layered structure of the mica powder, delaying gas phase combustion. At the same time, the polyphosphate generated by the decomposition of calcium hydrogen phosphate reacts with the Si-OH on the surface of the mica powder to form Si-OP covalent bonds, constructing a "ceramic" carbon layer barrier in the condensed phase. When the temperature exceeds 250°C, the interlayer hydrated ions of the mica powder are released and react with the phosphate substances decomposed by the flame retardant to form a low-melting point glass, which fills the pores of the carbon layer and reduces the heat release rate. In step S3, modified aluminum nitride fibers are blended with mica powder and flame retardant and dispersed in a 0.3-0.7T magnetic field, followed by the addition of boron nitride nanotubes for further ultrasonic blending. The core of magnetic field dispersion is to use the magnetic field to regulate the arrangement of the filler so that it forms a directional heat conduction channel in the matrix. Under the action of the magnetic field, aluminum nitride fibers can be arranged in a specific direction to form a continuous heat conduction path, reducing the interfacial thermal resistance between the fillers. The addition of boron nitride nanotubes, through its high thermal conductivity and low thermal expansion coefficient, synergizes with the modified aluminum nitride fibers during the ultrasonic blending process to form a multi-level heat conduction network. This treatment method can significantly improve the thermal conductivity of the sealant, while reducing the performance unevenness problem caused by filler aggregation through the uniform distribution of the filler. Step S4 is the last step in the preparation of the sealant, which is achieved by adding the thermally conductive filler and the remaining flame retardant to the matrix and stirring in a planetary mixer, and finally adding the isocyanate curing agent and performing vacuum degassing. The addition of an isocyanate curing agent reacts with the amino groups of the amino-terminated polyether to form a cross-linked polyurethane network, enhancing the material's mechanical strength and durability. The vacuum degassing step eliminates air bubbles and defects in the material, ensuring close contact between the filler and the matrix, thereby reducing interfacial thermal resistance and improving thermal conductivity. This treatment not only optimizes the material's microstructure but also improves the sealant's long-term service stability by reducing bubbles and defects.

[0032] The method of using the sealant of this application is closely related to its actual application in power battery modules. In the manufacturing process of power batteries, sealants are mainly used for bonding between battery cells and structural parts, as well as sealing between battery cells and module casings. Its specific method of use includes the following steps: first, applying the sealant to the surface of the battery cell or the bonding area of ​​the structural parts to ensure uniform coating thickness; second, curing under appropriate temperature and pressure conditions to form a stable cross-linked network of the sealant; finally, by testing its bonding strength and sealing performance, ensure its functionality in the battery module.

[0033] The application advantages of the thermally conductive flame-retardant sealant of this application in power battery modules are mainly reflected in its rapid heat conduction and effective suppression of combustion reactions. During the operation of the battery module, a large amount of heat is generated between the battery cells. Especially in high-power charging and discharging or thermal runaway scenarios, the accumulation of heat may cause the battery cell temperature to rise sharply, thereby triggering thermal runaway. The sealant can effectively address this problem through its multi-level thermal conductivity network and flame retardant mechanism. Modified aluminum nitride fibers and boron nitride nanotubes are dispersed by magnetic fields and ultrasonically treated to form continuous thermal conduction channels in the matrix. The high thermal conductivity and low thermal expansion coefficient of these fillers enable them to form an efficient heat conduction path in the matrix, reducing the interfacial thermal resistance. The layered structure of mica powder forms a multi-level thermal conduction network in the matrix through its flaky arrangement, further optimizing the thermal conductivity. Through the synergistic effect of these fillers, the sealant can quickly conduct the heat generated by the battery cells to other parts of the module, thereby reducing the risk of local overheating.

[0034] In thermal runaway scenarios, the flame retardant properties of the sealant are achieved through its multi-stage reaction mechanism. First, the polyglutamic acid-MCA core-shell structure decomposes through endothermic decomposition at the initial stage of combustion, reducing the temperature rise rate of the material and delaying the onset of the combustion reaction. Secondly, calcium hydrogen phosphate decomposes at high temperatures to produce calcium oxide and calcium phosphate, forming an inorganic protective layer that isolates the transfer of heat and oxygen, thereby inhibiting the further development of the combustion reaction. Finally, the hydroxyapatite coating layer, through its high melting point characteristics, provides an additional thermal barrier at high temperatures, reducing the thermal decomposition rate of the material. The synergistic effect of these mechanisms can significantly delay the combustion process, reduce the release of toxic gases, and thus improve the safety of the battery module.

[0035] The flame retardant and thermal conductivity properties of the sealant of the present application do not exist independently, but are achieved through the synergistic effect of the components. In terms of thermal conductivity, the uniform distribution of fillers and interface optimization enable heat to be conducted quickly, reducing local overheating. In terms of flame retardancy, the composite flame retardant delays the combustion process and reduces the release of toxic gases through a multi-stage reaction mechanism. The synergistic effect of the two is that the improvement of thermal conductivity can reduce the thermal resistance between battery cells, thereby reducing the risk of thermal runaway caused by heat accumulation, while the optimization of flame retardant properties can provide additional protection when thermal runaway occurs and delay the propagation of the combustion reaction. Through this collaborative design, the sealant can achieve efficient thermal management and safety assurance at the same time under the complex service conditions of the battery module.

[0036] The long-term service stability of the sealant is also the key to its reliability in power battery modules. Under high-frequency vibration and thermal cycling conditions, the performance of the material may decline due to filler sedimentation or interface failure. By optimizing the distribution and interface bonding of the filler, the sealant can maintain stable performance under these conditions. The introduction of silane coupling agent reduces the possibility of filler migration by enhancing the interface bonding between the filler and the matrix. Magnetic field dispersion and ultrasonic treatment reduce local performance degradation caused by filler aggregation by optimizing the distribution of the filler. In addition, the cross-linking effect of the isocyanate curing agent further improves the durability of the material, allowing it to maintain stable mechanical and thermal properties during long-term service. Through these designs, the sealant can ensure the long-term stability of its thermal conductivity and flame retardant properties under the complex service conditions of the battery module, thereby improving the safety and reliability of the battery.

[0037] In summary, the beneficial effects of this application are:

[0038] 1. The sealant of the present application significantly improves the thermal conductivity efficiency by introducing a composite thermal conductive system of modified aluminum nitride fibers, mica powder and boron nitride nanotubes, combined with magnetic field dispersion and ultrasonic blending technology. The modified aluminum nitride fibers are etched with NaOH to form nanogrooves, and the surface activity is enhanced by KH-550 treatment, so that they form a close bond with the matrix and reduce the interfacial thermal resistance; the layered structure of the mica powder and the low thermal expansion coefficient of the boron nitride nanotubes jointly construct a multi-level thermal conductive network. In terms of flame retardant properties, the polyglutamic acid-melamine cyanurate-calcium hydrogen phosphate composite flame retardant achieves efficient flame retardancy through a multi-stage reaction mechanism: in the early stage of combustion, the polyglutamic acid-MCA core-shell structure absorbs heat and decomposes to delay temperature rise; in the high-temperature stage, calcium hydrogen phosphate generates an inorganic protective layer to isolate heat and oxygen; in the event of thermal runaway, the hydroxyapatite coating further forms a thermal barrier to inhibit the spread of combustion.

[0039] 2. In this application, the terminal amino polyether and the lithium silicate glass ceramic precursor construct a flexible and stable hydrogen bond network matrix, and the cross-linking effect of the isocyanate curing agent enhances the overall strength of the material. The silane coupling agent optimizes the interface bonding between the filler and the matrix by grafting -PO(OH)2 groups, reducing the degradation of mechanical properties due to interface weakening. The vacuum degassing process eliminates internal bubble defects and ensures close contact between the filler and the matrix, thereby maintaining high tensile strength and elongation at break under high-frequency vibration and thermal cycling conditions. Magnetic field dispersion and ultrasonic treatment technology ensure uniform distribution of the filler, avoiding local performance unevenness caused by filler sedimentation or aggregation. In addition, the gradient stirring strategy and temperature control of the planetary mixer further optimize the microstructure of the material, enabling it to maintain stable bonding strength and sealing performance under complex working conditions.

[0040] 3. Through multi-level particle size compounding and interface optimization, the material of this application achieves a balance between thermal conductivity continuity and filler dispersion, avoiding performance fluctuations caused by the sedimentation of single particle size fillers. During thermal runaway, the inorganic protective layer formed by the material effectively inhibits the spread of combustion, while reducing smoke generation, significantly improving the overall safety of the battery system. In addition, the material does not significantly sacrifice bonding strength and flexibility due to the addition of fillers, and can adapt to slight deformations of the battery module caused by thermal expansion differences. Compared with traditional epoxy resin or polyurethane potting glue, the material of this application has significantly improved thermal conductivity, flame retardant grade and mechanical properties. At the same time, by optimizing the filler ratio and processing technology, the feasibility of large-scale application is improved. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below. Obviously, the embodiments described are part of the embodiments of the present invention, rather than all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art fall within the scope of protection of the present invention. It should be noted that the sources of raw materials not mentioned in the present invention may be commercially available or prepared by conventional methods, and the present invention is not limited to this.

[0042] The lithium aluminum silicate glass powder used in the following experiments was produced by Suzhou Qiuyi New Materials Co., Ltd., with a lithium-silicon ratio of 1:4 and a particle size of less than 10 μm.

[0043] Example 1

[0044] Preparation of lithium silicate glass ceramic precursor:

[0045] Weigh 100 g of lithium aluminosilicate glass powder containing 5 wt% ZnO, a lithium-silicon ratio of 1:4, and a particle size of <10 μm, place it in a three-necked flask, introduce nitrogen to exclude air, and slowly add phosphorus oxychloride into the flask at a mass ratio of glass powder to phosphorus oxychloride of 29:1. Stir and react in an oil bath at 70°C for 2 hours. After the reaction is completed, wash the product with deionized water three times, filter it, and vacuum dry it at 80°C for 12 hours to obtain a lithium silicate glass ceramic precursor with surface grafted -PO(OH)2 groups.

[0046] Preparation of polyglutamic acid-melamine cyanurate-calcium hydrogen phosphate composite flame retardant:

[0047] Step A: Dissolve 15 g of γ-polyglutamic acid and 10 g of melamine cyanurate in 100 mL of deionized water, adjust the pH to 9 with 1 mol / L NaOH solution, and stir and coprecipitate at 60°C for 2 h to form a polyglutamic acid-MCA core-shell structure. Filter and dry to obtain product A.

[0048] Step B: Product A and 12 g of calcium hydrogen phosphate were added to 200 mL of deionized water, and the pH was adjusted to 8 with 1 mol / L HCl. The mixture was subjected to a chelation reaction at 70°C for 3 h to form 50-100 nm nanoparticles, which were then centrifuged and dried to obtain Product B.

[0049] Step C: Prepare an electrolyte solution containing 140 mmol / L NaCl, 5 mmol / L KCl, 2.5 mmol / L CaCl2, 1 mmol / L MgCl2·6H2O, 4 mmol / L NaHCO3, and 1 mmol / L KH2PO4, with a pH of 7.4, add 5 wt% ammonium magnesium phosphate, add product B to the solution, and heat at 37°C for 24 h. After filtration and drying, a polyglutamic acid-melamine cyanurate-calcium hydrogen phosphate composite flame retardant is obtained.

[0050] Preparation of modified aluminum nitride fiber:

[0051] The aluminum nitride fiber was immersed in a 3wt% NaOH solution and etched at room temperature for 30 minutes to form a nano-groove with a depth of 20-50nm. The fiber was washed with water until neutral and then dried. The etched fiber was treated with a 2wt% KH-550 ethanol solution, stirred at 60°C for 1 hour, and filtered and dried. An electrolyte solution containing 0.5wt% PVA was prepared with the same composition as in the above step C. The fiber was added to the solution, stirred at room temperature for 4 hours, and filtered and dried to obtain the modified aluminum nitride fiber.

[0052] Sealant preparation method:

[0053] S1. Add 200 g of amino-terminated polyether with a molecular weight of 4000 to the reactor, raise the temperature to 85°C, add 100 g of lithium silicate glass ceramic precursor, and stir for 30 minutes; add 30 g of silane coupling agent (KH-550), continue stirring for 1 hour, and then add 30 g of TiO2 as a nanocrystal nucleating agent. Incubate the reaction until the system is uniform and transparent to obtain a hydrogen bond network matrix.

[0054] S2. Add 120 g of wet-ground phlogopite to 500 mL of 3 wt% KH-560-ethanol solution, stir at 75°C for 1.5 h, filter, wash twice with ethanol, and dry at 80°C for 4 h. Blend the dried mica powder and a polyglutamic acid-melamine cyanurate-calcium hydrogen phosphate composite flame retardant in a mass ratio of 1:0.3 in 300 mL of deionized water, ultrasonically disperse at a power of 300 W for 40 min, and then spray-dry at an inlet air temperature of 120°C to obtain a pretreated filler.

[0055] S3. Disperse 300 g of modified aluminum nitride fiber and the pretreated filler obtained in S2 in a 0.5 T magnetic field for 30 min to align the fibers; add 30 g of boron nitride nanotubes and ultrasonically blend them at a power of 400 W for 1.5 h to form a uniformly dispersed composite thermally conductive filler.

[0056] S4. Add the composite thermally conductive filler obtained in S3 and 130g of polyglutamic acid-melamine cyanurate-calcium hydrogen phosphate composite flame retardant to the matrix obtained in S1, place it in a planetary mixer, first stir at 50°C with a revolution of 150rpm and a rotation of 1200rpm for 30min, then heat to 90°C, stir at a revolution of 200rpm and a rotation of 1800rpm for 1h; add 70g of isocyanate curing agent, and then add 25g of terminal amino polyether with a molecular weight of 1000, degas at a vacuum degree of -0.085MPa for 20min to obtain a thermally conductive flame retardant sealant for power batteries.

[0057] Example 2

[0058] Preparation of lithium silicate glass ceramic precursor:

[0059] Weigh 100 g of lithium aluminosilicate glass powder containing 5 wt% ZnO, a lithium-silicon ratio of 1:4, and a particle size of <10 μm, place it in a three-necked flask, introduce nitrogen to exclude air, and slowly add phosphorus oxychloride into the flask at a mass ratio of 45:1 between glass powder and phosphorus oxychloride. Stir and react in a 70 ° C oil bath for 1 hour. After the reaction is completed, wash the product with deionized water 3 times, filter it, and vacuum dry it at 80 ° C for 12 hours to obtain a lithium silicate glass ceramic precursor with surface grafted -PO(OH)2 groups.

[0060] Preparation of polyglutamic acid-melamine cyanurate-calcium hydrogen phosphate composite flame retardant:

[0061] Step A: Dissolve 15 g of γ-polyglutamic acid and 10 g of melamine cyanurate in 100 mL of deionized water, adjust the pH to 9 with 1 mol / L NaOH solution, and stir and coprecipitate at 60°C for 2 h to form a polyglutamic acid-MCA core-shell structure. Filter and dry to obtain product A.

[0062] Step B: Product A and 12 g of calcium hydrogen phosphate were added to 200 mL of deionized water, and the pH was adjusted to 8 with 1 mol / L HCl. The mixture was subjected to a chelation reaction at 70°C for 3 h to form 50-100 nm nanoparticles, which were then centrifuged and dried to obtain product B.

[0063] Step C: Prepare an electrolyte solution containing 135 mmol / L NaCl, 4 mmol / L KCl, 2 mmol / L CaCl2, 0.8 mmol / L MgCl2·6H2O, 3.5 mmol / L NaHCO3, and 0.8 mmol / L KH2PO4, with a pH of 7.2, add 5 wt% ammonium magnesium phosphate, add product B to the solution, and heat at 37°C for 12 h. After filtration and drying, a polyglutamic acid-melamine cyanurate-calcium hydrogen phosphate composite flame retardant is obtained.

[0064] Preparation of modified aluminum nitride fiber:

[0065] The aluminum nitride fiber was immersed in a 1wt% NaOH solution and etched at room temperature for 30 minutes to form a nano-groove with a depth of 20-50nm. The fiber was washed with water until neutral and then dried. The etched fiber was treated with a 1wt% KH-550 ethanol solution, stirred at 60°C for 1 hour, and filtered and dried. An electrolyte solution containing 0.3wt% PVA was prepared with the same composition as in step C. The fiber was added to the solution, stirred at room temperature for 4 hours, and filtered and dried to obtain the modified aluminum nitride fiber.

[0066] Sealant preparation method:

[0067] S1. Add 150 g of amino-terminated polyether with a molecular weight of 3000 to a reactor, raise the temperature to 85°C, add 80 g of lithium silicate glass-ceramic precursor, and stir for 30 minutes; add 20 g of silane coupling agent (KH-550), continue stirring for 1 hour, then add TiO2, and keep the reaction warm until the system is uniform and transparent to obtain a hydrogen bond network matrix.

[0068] S2. Add 100 g of wet-ground phlogopite to 500 mL of 2 wt% KH-560-ethanol solution, stir at 70°C for 1 h, filter, wash twice with ethanol, and dry at 80°C for 4 h. Blend the dried mica powder and polyglutamic acid-melamine cyanurate-calcium hydrogen phosphate composite flame retardant in a mass ratio of 1:0.2 in 300 mL of deionized water, ultrasonically disperse at a power of 300 W for 30 min, and then spray-dry at an inlet air temperature of 120°C to obtain the pretreated filler.

[0069] S3. Disperse 270 g of modified aluminum nitride fiber and the pretreated filler obtained in S2 in a 0.3 T magnetic field for 30 min to align the fibers; add 30 g of boron nitride nanotubes and ultrasonically blend them at a power of 400 W for 1 h to form a uniformly dispersed composite thermally conductive filler.

[0070] S4. Add the composite thermal conductive filler obtained in S3 and 100g of polyglutamic acid-melamine cyanurate-calcium hydrogen phosphate composite flame retardant to the matrix obtained in S1, place it in a planetary mixer, first stir at 50°C with a revolution of 100rpm and a rotation of 1000rpm for 20min, then heat to 85°C, stir at a revolution of 150rpm and a rotation of 1500rpm for 0.5h; add 50g of isocyanate curing agent, without adding low molecular weight end amino polyether, degas at a vacuum degree of -0.08MPa for 15min to prepare the sealant.

[0071] Example 3

[0072] Preparation of lithium silicate glass ceramic precursor:

[0073] Weigh 200 g of lithium aluminosilicate glass powder containing 8 wt% ZnO, a lithium-silicon ratio of 1:4, and a particle size of <10 μm, place it in a three-necked flask, introduce nitrogen to exclude air, and slowly add phosphorus oxychloride into the flask at a mass ratio of glass powder to phosphorus oxychloride of 15:1. Stir and react in a 90°C oil bath for 3 hours. After the reaction is completed, wash the product with deionized water 3 times, filter it, and vacuum dry it at 80°C for 12 hours to obtain a lithium silicate glass ceramic precursor with surface grafted -PO(OH)2 groups.

[0074] Preparation of polyglutamic acid-melamine cyanurate-calcium hydrogen phosphate composite flame retardant:

[0075] Step A: Dissolve 25 g of γ-polyglutamic acid and 10 g of melamine cyanurate in 100 mL of deionized water, adjust the pH to 11 with 1 mol / L NaOH solution, and stir and coprecipitate at 60°C for 2 h to form a polyglutamic acid-MCA core-shell structure. Filter and dry to obtain product A.

[0076] Step B: Product A and 12 g of calcium hydrogen phosphate were added to 200 mL of deionized water, and the pH was adjusted to 10 with 1 mol / L HCl. The mixture was subjected to a chelation reaction at 70°C for 3 h to form 50-100 nm nanoparticles, which were then centrifuged and dried to obtain product B.

[0077] Step C: Prepare an electrolyte solution containing 150 mmol / L NaCl, 6 mmol / L KCl, 3 mmol / L CaCl2, 1.2 mmol / L MgCl2·6H2O, 5 mmol / L NaHCO3, and 1.2 mmol / L KH2PO4, with a pH of 7.6, add 10 wt% ammonium magnesium phosphate, add product B to the solution, and heat at 37°C for 36 h. After filtration and drying, a polyglutamic acid-melamine cyanurate-calcium hydrogen phosphate composite flame retardant is obtained.

[0078] Preparation of modified aluminum nitride fiber:

[0079] The aluminum nitride fiber was immersed in a 5wt% NaOH solution and etched at room temperature for 30 minutes to form a nano-groove with a depth of 20-50nm. The fiber was washed with water until neutral and then dried. The etched fiber was treated with a 3wt% KH-550 ethanol solution, stirred at 60°C for 1 hour, and filtered and dried. An electrolyte solution containing 0.7wt% PVA was prepared with the same composition as in step C. The fiber was added to the solution, stirred at room temperature for 4 hours, and filtered and dried to obtain the modified aluminum nitride fiber.

[0080] Sealant preparation method:

[0081] S1. Add 300 g of amino-terminated polyether with a molecular weight of 5000 to the reactor, raise the temperature to 95°C, add 180 g of lithium silicate glass ceramic precursor, and stir for 30 minutes; add 40 g of silane coupling agent (KH-550), continue stirring for 1 hour, and then add 50 g of TiO2 as a nanocrystal nucleating agent. Incubate the reaction until the system is uniform and transparent to obtain a hydrogen bond network matrix.

[0082] S2. Add 150 g of wet-ground phlogopite to 500 mL of 5 wt% KH-560-ethanol solution, stir at 80°C for 2 h, filter, wash twice with ethanol, and dry at 80°C for 4 h. Blend the dried mica powder and a polyglutamic acid-melamine cyanurate-calcium hydrogen phosphate composite flame retardant in a mass ratio of 1:0.5 in 300 mL of deionized water, ultrasonically disperse the mixture at a power of 500 W for 50 min, and then spray-dry at an inlet air temperature of 120°C to obtain a pretreated filler.

[0083] S3. Disperse 350 g of modified aluminum nitride fiber and the pretreated filler obtained in S2 in a 0.7 T magnetic field for 30 min to align the fibers; add 50 g of boron nitride nanotubes and ultrasonically blend them at a power of 400 W for 2 h to form a uniformly dispersed composite thermal conductive filler.

[0084] S4. Add the composite thermal conductive filler obtained in S3 and 145g of polyglutamic acid-melamine cyanurate-calcium hydrogen phosphate composite flame retardant to the matrix obtained in S1, place it in a planetary mixer, first stir at 70°C with a revolution of 200rpm and a rotation of 1500rpm for 40min, then heat to 95°C, stir at a revolution of 250rpm and a rotation of 2000rpm for 1.5h; add 90g of isocyanate curing agent, and then add 30g of terminal amino polyether with a molecular weight of 1200, degas at a vacuum degree of -0.09MPa for 30min to prepare a sealant.

[0085] Example 4

[0086] Preparation of lithium silicate glass ceramic precursor:

[0087] Weigh 200 g of lithium aluminosilicate glass powder containing 6.5 wt% ZnO, a lithium-silicon ratio of 1:4, and a particle size of <10 μm, place it in a three-necked flask, introduce nitrogen to exclude air, and slowly add phosphorus oxychloride into the flask at a mass ratio of 37:1 between glass powder and phosphorus oxychloride. Stir and react in an 80°C oil bath for 2 hours. After the reaction is completed, wash the product with deionized water 3 times, filter it, and vacuum dry it at 80°C for 12 hours to obtain a lithium silicate glass ceramic precursor with surface grafted -PO(OH)2 groups.

[0088] Preparation of polyglutamic acid-melamine cyanurate-calcium hydrogen phosphate composite flame retardant:

[0089] Step A: Dissolve 20 g of γ-polyglutamic acid and 10 g of melamine cyanurate in 100 mL of deionized water, adjust the pH to 10 with 1 mol / L NaOH solution, and stir and coprecipitate at 60°C for 2 h to form a polyglutamic acid-MCA core-shell structure. Filter and dry to obtain product A.

[0090] Step B: Product A and 12 g of calcium hydrogen phosphate were added to 200 mL of deionized water, and the pH was adjusted to 9 with 1 mol / L HCl. The mixture was subjected to a chelation reaction at 70°C for 3 h to form 50-100 nm nanoparticles, which were then centrifuged and dried to obtain product B.

[0091] Step C: Prepare an electrolyte solution containing 140 mmol / L NaCl, 5 mmol / L KCl, 2.5 mmol / L CaCl2, 1 mmol / L MgCl2·6H2O, 4 mmol / L NaHCO3, and 1 mmol / L KH2PO4, with a pH of 7.4, add 7.5 wt% ammonium magnesium phosphate, add product B to the solution, and heat at 37°C for 24 h. After filtration and drying, a polyglutamic acid-melamine cyanurate-calcium hydrogen phosphate composite flame retardant is obtained.

[0092] Preparation of modified aluminum nitride fiber:

[0093] The aluminum nitride fiber was immersed in a 3wt% NaOH solution and etched at room temperature for 30 minutes to form a nano-groove with a depth of 20-50nm. The fiber was washed with water until neutral and then dried. The etched fiber was treated with a 2wt% KH-550 ethanol solution, stirred at 60°C for 1 hour, and filtered and dried. An electrolyte solution containing 0.5wt% PVA was prepared with the same composition as in step C. The fiber was added to the solution, stirred at room temperature for 4 hours, and filtered and dried to obtain the modified aluminum nitride fiber.

[0094] Sealant preparation method:

[0095] S1. Add 225 g of amino-terminated polyether with a molecular weight of 4000 to a reactor, raise the temperature to 90°C, add 130 g of lithium silicate glass-ceramic precursor, and stir for 30 minutes. Add 30 g of silane coupling agent (KH-550), continue stirring for 1 hour, and keep the reaction warm until the system is uniform and transparent to obtain a hydrogen bond network matrix.

[0096] S2. Add 125 g of wet-ground phlogopite to 500 mL of 4 wt% KH-560-ethanol solution, stir at 78°C for 1.8 h, filter, wash twice with ethanol, and dry at 80°C for 4 h. Blend the dried mica powder and polyglutamic acid-melamine cyanurate-calcium hydrogen phosphate composite flame retardant in a mass ratio of 1:0.35 in 300 mL of deionized water, ultrasonically disperse at a power of 350 W for 45 min, and then spray-dry at an inlet air temperature of 120°C to obtain the pretreated filler.

[0097] S3. Disperse 300 g of modified aluminum nitride fiber and the pretreated filler obtained in S2 in a 0.5 T magnetic field for 30 min to align the fibers; add 40 g of boron nitride nanotubes and ultrasonically blend them at a power of 400 W for 1.5 h to form a uniformly dispersed composite thermally conductive filler.

[0098] S4. Add the composite thermal conductive filler obtained in S3 and 126g of polyglutamic acid-melamine cyanurate-calcium hydrogen phosphate composite flame retardant to the matrix obtained in S1, place it in a planetary mixer, first stir at 60°C with a revolution of 180rpm and a rotation of 1300rpm for 35min, then heat to 92°C, stir at a revolution of 220rpm and a rotation of 1700rpm for 1.2h; add 75g of isocyanate curing agent, and then add 28g of terminal amino polyether with a molecular weight of 1000, degas at a vacuum degree of -0.088MPa for 25min to prepare a sealant.

[0099] Comparative Example 1 does not add lithium silicate glass ceramic precursor, and does not add TiO 2， The rest is the same as in Example 1, and the method is as follows:

[0100] Preparation of polyglutamic acid-melamine cyanurate-calcium hydrogen phosphate composite flame retardant:

[0101] Step A: Dissolve 15 g of γ-polyglutamic acid and 10 g of melamine cyanurate in 100 mL of deionized water, adjust the pH to 9 with 1 mol / L NaOH solution, and stir and coprecipitate at 60°C for 2 h to form a polyglutamic acid-MCA core-shell structure. Filter and dry to obtain product A.

[0102] Step B: Product A and 12 g of calcium hydrogen phosphate were added to 200 mL of deionized water, and the pH was adjusted to 8 with 1 mol / L HCl. The mixture was subjected to a chelation reaction at 70°C for 3 h to form 50-100 nm nanoparticles, which were then centrifuged and dried to obtain Product B.

[0103] Step C: Prepare an electrolyte solution containing 140 mmol / L NaCl, 5 mmol / L KCl, 2.5 mmol / L CaCl2, 1 mmol / L MgCl2·6H2O, 4 mmol / L NaHCO3, and 1 mmol / L KH2PO4, with a pH of 7.4, add 5 wt% ammonium magnesium phosphate, add product B to the solution, and heat at 37°C for 24 h. After filtration and drying, a polyglutamic acid-melamine cyanurate-calcium hydrogen phosphate composite flame retardant is obtained.

[0104] Preparation of modified aluminum nitride fiber:

[0105] The aluminum nitride fiber was immersed in a 3wt% NaOH solution and etched at room temperature for 30 minutes to form a nano-groove with a depth of 20-50nm. The fiber was washed with water until neutral and then dried. The etched fiber was treated with a 2wt% KH-550 ethanol solution, stirred at 60°C for 1 hour, and filtered and dried. An electrolyte solution containing 0.5wt% PVA was prepared with the same composition as in the above step C. The fiber was added to the solution, stirred at room temperature for 4 hours, and filtered and dried to obtain the modified aluminum nitride fiber.

[0106] Sealant preparation method:

[0107] S1. Add 200 g of amino-terminated polyether with a molecular weight of 4000 to the reactor, raise the temperature to 85°C, add 30 g of silane coupling agent (KH-550), continue stirring for 1 hour, and keep the temperature to react until the system is uniform and transparent to obtain a hydrogen bond network matrix.

[0108] S2. Add 120 g of wet-ground phlogopite to 500 mL of 3 wt% KH-560-ethanol solution, stir at 75°C for 1.5 h, filter, wash twice with ethanol, and dry at 80°C for 4 h. Blend the dried mica powder and a polyglutamic acid-melamine cyanurate-calcium hydrogen phosphate composite flame retardant in a mass ratio of 1:0.3 in 300 mL of deionized water, ultrasonically disperse at a power of 300 W for 40 min, and then spray-dry at an inlet air temperature of 120°C to obtain a pretreated filler.

[0109] S3. Disperse 300 g of modified aluminum nitride fiber and the pretreated filler obtained in S2 in a 0.5 T magnetic field for 30 min to align the fibers; add 30 g of boron nitride nanotubes and ultrasonically blend them at a power of 400 W for 1.5 h to form a uniformly dispersed composite thermally conductive filler.

[0110] S4. Add the composite thermally conductive filler obtained in S3 and 130g of polyglutamic acid-melamine cyanurate-calcium hydrogen phosphate composite flame retardant to the matrix obtained in S1, place it in a planetary mixer, first stir at 50°C with a revolution of 150rpm and a rotation of 1200rpm for 30min, then heat to 90°C, stir at a revolution of 200rpm and a rotation of 1800rpm for 1h; add 70g of isocyanate curing agent, and then add 25g of terminal amino polyether with a molecular weight of 1000, degas at a vacuum degree of -0.085MPa for 20min to obtain a thermally conductive flame retardant sealant for power batteries.

[0111] Comparative Example 2 uses the same weight of aluminum hydroxide instead of the composite flame retardant, and does not mix it with mica. The rest is the same as Example 1.

[0112] Preparation of lithium silicate glass ceramic precursor:

[0113] Weigh 100 g of lithium aluminosilicate glass powder containing 5 wt% ZnO, a lithium-silicon ratio of 1:4, and a particle size of <10 μm, place it in a three-necked flask, introduce nitrogen to exclude air, and slowly add 23.7 g (0.156 mol) of phosphorus oxychloride into the flask at a molar ratio of glass powder to phosphorus oxychloride of 1:0.2. Stir and react in an oil bath at 70 ° C for 2 h. After the reaction is completed, wash the product with deionized water 3 times, filter it, and vacuum dry it at 80 ° C for 12 h to obtain a lithium silicate glass ceramic precursor with surface grafted -PO(OH)2 groups.

[0114] Preparation of modified aluminum nitride fiber:

[0115] The aluminum nitride fiber was immersed in a 3wt% NaOH solution and etched at room temperature for 30 minutes to form a nano-groove with a depth of 20-50nm. The fiber was washed with water until neutral and then dried. The etched fiber was treated with a 2wt% KH-550 ethanol solution, stirred at 60°C for 1 hour, and filtered and dried. An electrolyte solution containing 0.5wt% PVA was prepared, the fiber was added to the solution, stirred at room temperature for 4 hours, and filtered and dried to obtain the modified aluminum nitride fiber.

[0116] Sealant preparation method:

[0117] S1. Add 200 g of amino-terminated polyether with a molecular weight of 4000 to the reactor, raise the temperature to 85°C, add 100 g of lithium silicate glass ceramic precursor, and stir for 30 minutes; add 30 g of silane coupling agent (KH-550), continue stirring for 1 hour, and then add 30 g of TiO2 as a nanocrystal nucleating agent. Incubate the reaction until the system is uniform and transparent to obtain a hydrogen bond network matrix.

[0118] S2. Add 120 g of wet-ground phlogopite to 500 mL of 3 wt% KH-560-ethanol solution, stir at 75°C for 1.5 h, filter, wash twice with ethanol, and dry at 80°C for 4 h to obtain the pretreated filler.

[0119] S3. Disperse 300 g of modified aluminum nitride fiber and the pretreated filler obtained in S2 in a 0.5 T magnetic field for 30 min to align the fibers; add 30 g of boron nitride nanotubes and ultrasonically blend them at a power of 400 W for 1.5 h to form a uniformly dispersed composite thermally conductive filler.

[0120] S4. Add the composite thermally conductive filler and aluminum hydroxide obtained in S3 to the matrix obtained in S1, place it in a planetary mixer, first stir at 50°C with a revolution of 150 rpm and a rotation of 1200 rpm for 30 minutes, then heat to 90°C, stir at a revolution of 200 rpm and a rotation of 1800 rpm for 1 hour; add 70 g of isocyanate curing agent, and then add 25 g of terminal amino polyether with a molecular weight of 1000, degas at a vacuum degree of -0.085 MPa for 20 minutes to obtain a thermally conductive flame retardant sealant for power batteries.

[0121] Comparative Example 3 uses unmodified aluminum nitride fiber, and the rest is the same as Example 1.

[0122] Preparation of lithium silicate glass ceramic precursor:

[0123] Weigh 100 g of lithium aluminosilicate glass powder containing 5 wt% ZnO, a lithium-silicon ratio of 1:4, and a particle size of <10 μm, place it in a three-necked flask, introduce nitrogen to exclude air, and slowly add 23.7 g (0.156 mol) of phosphorus oxychloride into the flask at a molar ratio of glass powder to phosphorus oxychloride of 1:0.2. Stir and react in an oil bath at 70 ° C for 2 h. After the reaction is completed, wash the product with deionized water 3 times, filter it, and vacuum dry it at 80 ° C for 12 h to obtain a lithium silicate glass ceramic precursor with surface grafted -PO(OH)2 groups.

[0124] Preparation of polyglutamic acid-melamine cyanurate-calcium hydrogen phosphate composite flame retardant:

[0125] Step A: Dissolve 15 g of γ-polyglutamic acid and 10 g of melamine cyanurate in 100 mL of deionized water, adjust the pH to 9 with 1 mol / L NaOH solution, and stir and coprecipitate at 60°C for 2 h to form a polyglutamic acid-MCA core-shell structure. Filter and dry to obtain product A.

[0126] Step B: Product A and 12 g of calcium hydrogen phosphate were added to 200 mL of deionized water, and the pH was adjusted to 8 with 1 mol / L HCl. The mixture was subjected to a chelation reaction at 70°C for 3 h to form 50-100 nm nanoparticles, which were then centrifuged and dried to obtain Product B.

[0127] Step C: Prepare an electrolyte solution containing 140 mmol / L NaCl, 5 mmol / L KCl, 2.5 mmol / L CaCl2, 1 mmol / L MgCl2·6H2O, 4 mmol / L NaHCO3, and 1 mmol / L KH2PO4, with a pH of 7.4, add 5 wt% ammonium magnesium phosphate, add product B to the solution, and heat at 37°C for 24 h. After filtration and drying, a polyglutamic acid-melamine cyanurate-calcium hydrogen phosphate composite flame retardant is obtained.

[0128] Sealant preparation method:

[0129] S1. Add 200 g of amino-terminated polyether with a molecular weight of 4000 to the reactor, raise the temperature to 85°C, add 100 g of lithium silicate glass ceramic precursor, and stir for 30 minutes; add 30 g of silane coupling agent (KH-550), continue stirring for 1 hour, and then add 30 g of TiO2 as a nanocrystal nucleating agent. Incubate the reaction until the system is uniform and transparent to obtain a hydrogen bond network matrix.

[0130] S2. Add 120 g of wet-ground phlogopite to 500 mL of 3 wt% KH-560-ethanol solution, stir at 75°C for 1.5 h, filter, wash twice with ethanol, and dry at 80°C for 4 h. Blend the dried mica powder and a polyglutamic acid-melamine cyanurate-calcium hydrogen phosphate composite flame retardant in a mass ratio of 1:0.3 in 300 mL of deionized water, ultrasonically disperse at a power of 300 W for 40 min, and then spray-dry at an inlet air temperature of 120°C to obtain a pretreated filler.

[0131] S3. Disperse 300 g of aluminum nitride fibers and the pretreated filler obtained in S2 in a 0.5 T magnetic field for 30 min to orient the fibers; add 30 g of boron nitride nanotubes and ultrasonically blend them at a power of 400 W for 1.5 h to form a uniformly dispersed composite thermally conductive filler.

[0132] S4. Add the composite thermally conductive filler obtained in S3 and 130g of polyglutamic acid-melamine cyanurate-calcium hydrogen phosphate composite flame retardant to the matrix obtained in S1, place it in a planetary mixer, first stir at 50°C with a revolution of 150rpm and a rotation of 1200rpm for 30min, then heat to 90°C, stir at a revolution of 200rpm and a rotation of 1800rpm for 1h; add 70g of isocyanate curing agent, and then add 25g of terminal amino polyether with a molecular weight of 1000, degas at a vacuum degree of -0.085MPa for 20min to obtain a thermally conductive flame retardant sealant for power batteries.

[0133] Comparative Example 4: The lithium silicate glass ceramic precursor is not reacted with phosphorus oxychloride for grafting, and the rest is the same as Example 1.

[0134] Preparation of polyglutamic acid-melamine cyanurate-calcium hydrogen phosphate composite flame retardant:

[0135] Step A: Dissolve 15 g of γ-polyglutamic acid and 10 g of melamine cyanurate in 100 mL of deionized water, adjust the pH to 9 with 1 mol / L NaOH solution, and stir and coprecipitate at 60°C for 2 h to form a polyglutamic acid-MCA core-shell structure. Filter and dry to obtain product A.

[0136] Step B: Product A and 12 g of calcium hydrogen phosphate were added to 200 mL of deionized water, and the pH was adjusted to 8 with 1 mol / L HCl. The mixture was subjected to a chelation reaction at 70°C for 3 h to form 50-100 nm nanoparticles, which were then centrifuged and dried to obtain Product B.

[0137] Step C: Prepare an electrolyte solution containing 140 mmol / L NaCl, 5 mmol / L KCl, 2.5 mmol / L CaCl2, 1 mmol / L MgCl2·6H2O, 4 mmol / L NaHCO3, and 1 mmol / L KH2PO4, with a pH of 7.4, add 5 wt% ammonium magnesium phosphate, add product B to the solution, and heat at 37°C for 24 h. After filtration and drying, a polyglutamic acid-melamine cyanurate-calcium hydrogen phosphate composite flame retardant is obtained.

[0138] Preparation of modified aluminum nitride fiber:

[0139] The aluminum nitride fiber was immersed in a 3wt% NaOH solution and etched at room temperature for 30 minutes to form a nano-groove with a depth of 20-50nm. The fiber was washed with water until neutral and then dried. The etched fiber was treated with a 2wt% KH-550 ethanol solution, stirred at 60°C for 1 hour, and filtered and dried. An electrolyte solution containing 0.5wt% PVA was prepared with the same composition as in the above step C. The fiber was added to the solution, stirred at room temperature for 4 hours, and filtered and dried to obtain the modified aluminum nitride fiber.

[0140] Sealant preparation method:

[0141] S1. Add 200 g of amino-terminated polyether with a molecular weight of 4000 to the reactor, raise the temperature to 85°C, add 100 g of lithium silicate glass ceramic precursor, and stir for 30 minutes; add 30 g of silane coupling agent (KH-550), continue stirring for 1 hour, and then add 30 g of TiO2 as a nanocrystal nucleating agent. Incubate the reaction until the system is uniform and transparent to obtain a hydrogen bond network matrix.

[0142] S2. Add 120 g of wet-ground phlogopite to 500 mL of 3 wt% KH-560-ethanol solution, stir at 75°C for 1.5 h, filter, wash twice with ethanol, and dry at 80°C for 4 h. Blend the dried mica powder and a polyglutamic acid-melamine cyanurate-calcium hydrogen phosphate composite flame retardant in a mass ratio of 1:0.3 in 300 mL of deionized water, ultrasonically disperse at a power of 300 W for 40 min, and then spray-dry at an inlet air temperature of 120°C to obtain a pretreated filler.

[0143] S3. Disperse 300 g of modified aluminum nitride fiber and the pretreated filler obtained in S2 in a 0.5 T magnetic field for 30 min to align the fibers; add 30 g of boron nitride nanotubes and ultrasonically blend them at a power of 400 W for 1.5 h to form a uniformly dispersed composite thermally conductive filler.

[0144] S4. Add the composite thermally conductive filler obtained in S3 and 130g of polyglutamic acid-melamine cyanurate-calcium hydrogen phosphate composite flame retardant to the matrix obtained in S1, place it in a planetary mixer, first stir at 50°C with a revolution of 150rpm and a rotation of 1200rpm for 30min, then heat to 90°C, stir at a revolution of 200rpm and a rotation of 1800rpm for 1h; add 70g of isocyanate curing agent, and then add 25g of terminal amino polyether with a molecular weight of 1000, degas at a vacuum degree of -0.085MPa for 20min to obtain a thermally conductive flame retardant sealant for power batteries.

[0145] The above embodiments and comparative examples were subjected to performance tests:

[0146] Thermal conductivity was measured using the laser flash method with a sample size of 10 mm × 10 mm × 2 mm and a test temperature of 25 °C.

[0147] The flame retardancy rating is determined by a vertical combustion test with a sample size of 125 mm × 13 mm × 1.6 mm. The flame is applied twice (10 seconds each time) and the afterburning time and dripping conditions are recorded.

[0148] The tensile properties were tested using a universal material testing machine, dumbbell-type specimens, a tensile speed of 50 mm / min, and a test temperature of 23°C ± 2°C.

[0149] Thermal cycling stability was tested using a high and low temperature alternating chamber (-40°C / 2h→150°C / 2h as one cycle), and the change rate of tensile strength was tested after 500 cycles.

[0150]

[0151] According to the above results, it can be seen that the amount of precursor and filler used in Example 2 is the minimum, the density of the interface bonding points is low, and the difference in expansion coefficient between the filler and the matrix during the thermal cycle causes microcracks, but does not completely destroy the thermal conduction path. After omitting the lithium silicate glass ceramic precursor in Comparative Example 1, the filler and the matrix are only combined by physical adsorption. The interface debonding occurs during the thermal cycle due to the mismatch of the expansion coefficient, and the thermal conduction network is completely destroyed. Comparative Example 2 uses a single aluminum hydroxide filler with weak interface bonding with the matrix. The high filling amount causes stress concentration in the system. The bubble defects expand into cracks during the thermal cycle, and the performance deteriorates sharply. Comparative Example 3 uses unmodified aluminum nitride fiber. Due to weak interface bonding, micro-displacement occurs during the thermal cycle, resulting in a break in the thermal conduction path; the settled filler agglomerates further aggravate the local thermal resistance. Comparative Example 4 uses an unmodified lithium silicate glass ceramic precursor with high surface energy. It agglomerates due to weak hydrogen bonding during thermal cycling, and gaps are formed between the agglomerates and the matrix, which become the origin of cracks. There is no -PO(OH)2 group catalysis, and the formation of the ceramic layer is delayed at high temperature. The density of the carbon layer decreases during combustion, and the flame retardant grade drops from V-0 to V-1.

Claims

1. Thermally conductive flame retardant sealant for power batteries, characterized in that: Includes the following components: 15-30 parts of amino-terminated polyether, 8-18 parts of lithium silicate glass ceramic precursor, 12-22 parts of polyglutamic acid-melamine cyanurate-calcium hydrogen phosphate composite flame retardant, 40-55 parts of composite thermal conductive filler, 2-4 parts of silane coupling agent, 5-9 parts of isocyanate curing agent; The composite thermally conductive filler comprises: 27-35 parts of modified aluminum nitride fiber, 10-15 parts of mica powder, and 3-5 parts of boron nitride nanotubes; The lithium silicate glass ceramic precursor is lithium aluminum silicate glass powder, which also includes 5-8wt% ZnO. The surface of the lithium aluminum silicate glass powder is grafted with -PO(OH)2 groups. The grafting method is to react the lithium aluminum silicate glass powder with phosphorus oxychloride in a molar ratio of 1:0.1-0.3 in a nitrogen atmosphere at 70-90°C for 1-3h, and then wash and dry. The polyglutamic acid-melamine cyanurate-calcium hydrogen phosphate composite flame retardant is prepared by the following method: A. co-precipitating γ-polyglutamic acid and melamine cyanurate at a mass ratio of 1.5-2.5:1 at a pH of 9-11 to form a polyglutamic acid-MCA core-shell structure; B. The product obtained in step A is chelated with calcium hydrogen phosphate at a pH of 8-10 to form nanoparticles of 50-100 nm; C. adding 5-10% magnesium ammonium phosphate to an electrolyte solution containing 135-150 mmol / L NaCl, 4-6 mmol / L KCl, 2-3 mmol / L CaCl2, 0.8-1.2 mmol / L MgCl2·6H2O, 3.5-5 mmol / L NaHCO3, and 0.8-1.2 mmol / L KH2PO4 at a pH of 7.2-7.6, and treating at 37°C for 12-36 hours to form a hydroxyapatite coating layer; The preparation method of the modified aluminum nitride fiber is as follows: Aluminum nitride fibers were etched with a 1-5wt% NaOH solution to form nanogrooves with a depth of 20-50nm, then treated with a 1-3wt% KH-550 solution, and then treated in an electrolyte solution containing 0.3-0.7wt% PVA, wherein the electrolyte solution contained 135-150mmol / L NaCl, 4-6mmol / L KCl, 2-3mmol / L CaCl2, 0.8-1.2mmol / L MgCl2·6H2O, 3.5-5mmol / L NaHCO3, and 0.8-1.2mmol / L KH2PO4, with a pH of 7.2-7.

6.

2. A method for preparing the thermally conductive flame-retardant sealant for power batteries according to claim 1, characterized in that: The following steps are involved: S1. A molecular weight of 3000-5000 amino-terminated polyether is mixed with a lithium silicate glass ceramic precursor at 85-95 ° C, a silane coupling agent is added, and after the reaction is completed, a hydrogen bond network matrix is ​​obtained; S2. The wet-ground phlogopite was added to a 2-5wt% KH-560 ethanol solution and stirred at 70-80 ° C for 1-2h. After washing and drying, the mica powder was mixed with a polyglutamic acid - melamine cyanurate - calcium hydrogen phosphate composite flame retardant in a mass ratio of 1:0.2-0.5 in deionized water and ultrasonically dispersed for 30-50min and dried for later use. S3 disperses the modified aluminum nitride fiber and the product obtained in S2 in a 0.3-0.7T magnetic field, then adds boron nitride nanotubes and ultrasonically blends for 1-2 hours; S4. Add the product obtained in S3 and the remaining polyglutamic acid-melamine cyanurate-calcium hydrogen phosphate composite flame retardant to the matrix obtained in S1, stir at 50-70°C for 20-40 minutes at a revolution of 100-200 rpm and a rotation of 1000-1500 rpm in a planetary mixer, heat to 85-95°C, stir at a revolution of 150-250 rpm and a rotation of 1500-2000 rpm for 0.5-1.5 hours, add isocyanate curing agent, and degas at a vacuum degree of -0.08-0.09 MPa for 15-30 minutes to prepare a sealant.

3. The method for preparing the thermally conductive flame-retardant sealant for power batteries according to claim 2, characterized in that: After adding the isocyanate curing agent in step S4, 2-3 parts of amino-terminated polyether with a molecular weight of 800-1200 are added.

4. The method for preparing the thermally conductive flame-retardant sealant for power batteries according to claim 2, characterized in that: After adding the silane coupling agent in step S1, 2-5 parts of TiO2 are added as a nanocrystal nucleating agent.

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