Heat-conducting flame-retardant difunctional power battery sealant and preparation method thereof

Abstract

The invention belongs to the field of sealants, and particularly relates to a heat-conducting flame-retardant difunctional power battery sealant and a preparation method thereof. Vulcanized silicone rubber is used as a matrix, a heat conduction system constructs a heat conduction path through alpha-aluminum oxide and boron nitride, a transverse enhanced network is formed in cooperation with the graphene nanosheets, the interface thermal resistance is reduced, and uniform diffusion of heat between battery cells is achieved. The flame-retardant system is prepared from expandable graphite, a coated melamine polyphosphate / tannic acid intercalated nickel aluminum hydrotalcite flame retardant and magnesium hydroxide. The preparation process adopts gradient stirring, vacuum defoaming and precise curing control to ensure uniform dispersion of components and structural densification. The sealant provided by the invention realizes physical isolation, chemical inhibition and thermal shielding synergistic protection in the whole stage of thermal runaway of the power battery, significantly reduces local hot spot risk and chain reaction probability, improves safety and prolongs the service life.

Description

Technical Field

[0001] The present application relates to the field of sealants, and in particular to a thermally conductive and flame-retardant dual-function power battery sealant and a preparation method thereof. Background Art

[0002] Amid the rapid development of the new energy vehicle industry, power batteries, as core components, have a significant impact on the safety and reliability of the vehicle. Sealant, a key material in the power battery packaging system, fulfills crucial functions such as waterproofing, dustproofing, shockproofing, and interface protection, playing an irreplaceable role in the long-term stable operation of the battery. As the energy and power densities of power batteries continue to increase, the heat generated during operation increases significantly. Furthermore, the complex electrochemical environment within the battery and the potential risk of thermal runaway place even more stringent requirements on the thermal conductivity and flame retardancy of the sealant.

[0003] During the charge and discharge cycle, especially at high rates, power batteries will continuously generate a large amount of heat. If the heat cannot be transferred to the heat dissipation system in a timely manner through the sealant, it is very easy to cause the local temperature of the battery to be too high, which will not only accelerate the aging of the electrode material and the decomposition of the electrolyte, but may also cause thermal runaway and pose a safety hazard. However, the thermal conductivity of silicone rubber-based sealants currently widely used on the market is often difficult to meet the needs of high-energy-density batteries. This type of sealant mostly relies on a single or low-efficiency thermal conductive filler. Due to the uneven dispersion of the filler or the insufficient construction of the thermal conductive path, its thermal conductivity is generally lower than 1.0W / (m·K), which cannot form an efficient heat transfer path and is difficult to meet the growing heat dissipation needs of power batteries.

[0004] In addition to thermal conductivity, flame retardancy is another key factor in ensuring the safety of power battery sealants. Under abnormal operating conditions, power batteries may experience short circuits or overcharge, leading to localized high temperatures or even flames. In these situations, sealants need to possess excellent flame retardancy to slow the spread of fire and reduce the risk of thermal runaway. However, existing sealants often use a single flame retardant, such as magnesium hydroxide. These flame retardants require high loadings to achieve a basic flame retardant effect. This high loading not only significantly reduces the sealant's mechanical properties, such as flexibility and tensile strength, making it susceptible to cracking during vibration or temperature cycling, but also significantly increases the system's viscosity, affecting the stability of processes such as mixing and extrusion. Furthermore, high loadings significantly increase the sealant's viscosity, making it difficult to mix evenly during mixing and degassing. This makes defects such as bubbles and missing adhesives more likely to occur during molding, severely impacting product consistency and hindering large-scale production. Furthermore, traditional flame retardants are prone to decomposition and failure at high temperatures, with some materials even producing droplets, which can trigger secondary combustion, making it difficult to meet the high-level flame retardancy required for power batteries. At the same time, the operating environment of power batteries experiences significant temperature fluctuations. During long-term use, sealants must maintain stable sealing properties at relatively high temperatures. Traditional silicone rubber-based sealants are susceptible to thermal oxidative aging when used at temperatures above 150°C. This can lead to molecular chain breakage, a decrease in crosslink density, increased material hardness, and a loss of elasticity. This can lead to cracks in the sealing interface, making it impossible to effectively prevent moisture, dust, and other impurities from invading the battery, severely impacting the lifespan and safety of the power battery.

[0005] In summary, current power battery sealants still face many challenges in performance balance. Traditional products have insufficient thermal conductivity and cannot meet heat dissipation requirements. In pursuit of flame retardant effects, they sacrifice the mechanical properties and processability of materials. They have poor stability in high-temperature environments and are difficult to work reliably for a long time. Summary of the Invention

[0006] In order to solve the above problems, the present application provides a thermally conductive and flame-retardant dual-function power battery sealant and its preparation method, which adopts a collaborative design of a vulcanized silicone rubber matrix and α-alumina / boron nitride thermal conductive filler, combined with a tannic acid intercalated nickel-aluminum hydrotalcite flame retardant and a gradient activated flame retardant system to achieve thermal conduction path construction and thermal runaway protection. The hydrogen bonding effect between tannic acid and the matrix is ​​enhanced through a weakly alkaline environment, eliminating the interfacial thermal resistance and improving the self-repair ability of microcracks. At the same time, the flame retardant system forms a physical isolation layer in the low temperature zone and catalyzes the generation of a dense composite carbon layer in the high temperature zone, effectively inhibiting molten droplets and secondary combustion. The preparation process ensures uniform dispersion of the components, takes into account low-viscosity processability and high mechanical properties, maintains elasticity in a wide temperature range, and significantly improves the sealing reliability and thermal runaway safety of the power battery.

[0007] The present application provides a thermally conductive and flame-retardant dual-function power battery sealant, which comprises the following components in parts by mass:

[0008] 100 parts of vulcanized silicone rubber, 15-45 parts of thermal conductive filler, 2-6 parts of magnesium hydroxide, 1-4 parts of expandable graphite, 1-4 parts of coated melamine polyphosphate / tannic acid intercalated nickel aluminum hydrotalcite flame retardant, and 0.3-1.2 parts of graphene nanosheets;

[0009] The thermally conductive filler comprises 12-33 parts of α-alumina and 4-11 parts of boron nitride;

[0010] The coated melamine polyphosphate / tannic acid intercalated nickel aluminum hydrotalcite flame retardant consists of a layered nickel aluminum hydrotalcite main body, an interlayer intercalant and a surface coating layer. The nickel-aluminum molar ratio of the layered nickel aluminum hydrotalcite is 15-2.5:1, the interlayer intercalant is tannic acid and melamine polyphosphate, and the surface coating layer is polydimethylsiloxane.

[0011] Furthermore, in the thermally conductive filler, the mass ratio of α-alumina to boron nitride is 2-6:1.

[0012] Furthermore, the preparation method of the coated melamine polyphosphate / tannic acid intercalated nickel aluminum hydrotalcite flame retardant is:

[0013] A. Add nickel-aluminum hydrotalcite to deionized water at a solid-to-liquid ratio of 1:10-20, add tannic acid at a mass ratio of tannic acid to nickel-aluminum hydrotalcite of 2.5-3.5:10, and ultrasonically disperse for 20-40 minutes. Adjust the pH to 8.0-9.0 with aqueous ammonia. Transfer the mixture to a reactor and hydrothermally react at 80-100°C for 5-7 hours. Filter, wash, and dry to obtain tannic acid-intercalated nickel-aluminum hydrotalcite.

[0014] B. Mixing the product obtained in step A with melamine polyphosphate in a mass ratio of 1.8-2.2:1 in deionized water at a solid-to-liquid ratio of 1:8-12, stirring at 45-55° C. for 7-9 hours, performing a hydrothermal intercalation reaction, filtering, washing, and drying to obtain a melamine polyphosphate / tannic acid intercalated nickel-aluminum hydrotalcite;

[0015] C. The product obtained in step B is immersed in an ethyl acetate solution of 8-12 wt% polydimethylsiloxane for 1-3 hours, taken out and cured at 75-85°C for 2-4 hours to form a polydimethylsiloxane surface coating layer, and then placed in a vacuum oven, heated at 110-130°C for 1.5-2.5 hours, then heated to 190-210°C for 0.5-1.5 hours, and cooled to obtain a coated melamine polyphosphate / tannic acid intercalated nickel aluminum hydrotalcite flame retardant.

[0016] Furthermore, the viscosity of the vulcanized silicone rubber is 25,000-35,000 cps, the particle size of the α-alumina is 5-50 μm, the particle size of the boron nitride is 50-200 nm, and the thickness of the graphene nanosheet is ≤5 nm.

[0017] The present application also provides a method for preparing the thermally conductive and flame-retardant dual-function power battery sealant, comprising the following steps:

[0018] S1. Synthesis of vulcanized silicone rubber: Octamethylcyclotetrasiloxane was used as the raw material. Water and tetramethylammonium hydroxide catalyst were added. The mixture was stirred at 80-90°C under nitrogen for 4-6 hours to obtain an α,ω-dihydroxypolydimethylsiloxane base rubber. The base rubber was then mixed with tetraethyl orthosilicate and dibutyltin dilaurate and stirred to obtain a room temperature paste-like vulcanized silicone rubber.

[0019] S2. The expandable graphite and coated melamine polyphosphate / tannic acid intercalated nickel aluminum hydrotalcite flame retardant mixed, added to a high-speed mixer 3000-4000rpm stirring for 20-30 minutes;

[0020] S3. α-alumina and boron nitride are added to the vulcanized silicone rubber obtained in step S1 and stirred at 5000-6000 rpm for 30-40 minutes to form a thermally conductive matrix;

[0021] S4. The mixture obtained in step S2, magnesium hydroxide, and graphene nanosheets are sequentially added to the thermally conductive substrate of step S3 and stirred for 1-1.5 hours;

[0022] S5. Degas the mixture of step S4 under a vacuum degree of -0.08 to -0.1 MPa for 20-40 minutes, and add 1-3% of the mass of the mixture obtained in step S4 to cure it.

[0023] Furthermore, in step S4, gradient stirring is adopted when each component is added: first stirring at a low speed of 1000-2000 rpm for 10 minutes, and then stirring at a high speed of 5000-6000 rpm for a total time of 1-1.5 hours.

[0024] Furthermore, in step S5, the curing agent is dibutyltin dilaurate, the curing temperature is 24-80° C., and the curing time is 1.5-24 hours.

[0025] Furthermore, in step S1, the amount of water added is 5%-8% of the mass of octamethylcyclotetrasiloxane, the amount of tetramethylammonium hydroxide added is 0.1%-0.3% of the mass of octamethylcyclotetrasiloxane, the amount of ethyl orthosilicate added is 3%-5% of the mass of octamethylcyclotetrasiloxane, and the amount of dibutyltin dilaurate added is 0.5%-1% of the mass of octamethylcyclotetrasiloxane.

[0026] As the base material of sealant, vulcanized silicone rubber plays the role of building the overall structural framework in the power battery packaging system. Its molecular chain has unique flexibility and a three-dimensional network structure formed by cross-linking. During the preparation process, octamethylcyclotetrasiloxane is used as the raw material. Water and tetramethylammonium hydroxide are added as catalysts to react under nitrogen to form an α,ω-dihydroxypolydimethylsiloxane base rubber. This base rubber is then mixed with tetraethyl orthosilicate and dibutyltin dilaurate. The tetraethyl orthosilicate acts as a crosslinker, undergoing a condensation reaction with the hydroxyl groups of the base rubber, while the dibutyltin dilaurate catalyzes this reaction and accelerates the crosslinking process. The two work synergistically to form a vulcanized silicone rubber that is paste-like at room temperature. Its viscosity is controlled between 25,000 and 35,000 cps. This viscosity range ensures stable mixing and extrusion during processing, preventing flow caused by too low viscosity or uneven mixing caused by too high viscosity. It also forms a tightly fitting sealant at the complex packaging interfaces of power batteries, such as the gap between the cell and the casing and around the terminal, effectively blocking the intrusion of moisture and dust. Its elasticity also allows it to withstand the vibration and impact of vehicle driving, maintaining interfacial sealing under temperature fluctuations from -40°C to 150°C, thus addressing the aging and cracking problems of traditional sealants at high temperatures.

[0027] The thermally conductive filler is composed of α-alumina and boron nitride in a mass ratio of 2-6:1. The particle size of α-alumina is 5-50μm, which is a large-particle filler. It can construct a macroscopic thermal conductive path in the matrix, providing a main channel for rapid heat transfer. The particle size of boron nitride is 50-200nm. As a small-particle filler, it can fill the microscopic gaps between large-particle α-alumina, reducing interfacial obstructions during heat transfer. The synergistic effect of the two significantly reduces interfacial thermal resistance. The introduction of graphene nanosheets further enhances the thermal conductivity of the sealant. Its two-dimensional layered structure can form an enhanced network for lateral thermal conductivity in the matrix. The interaction between the layers and the hydrogen bonding interaction of the silicone rubber molecular chains jointly construct a continuous thermal conductive path, which makes up for the shortcomings of traditional single fillers in lateral heat transfer. Inside a power battery, heat not only needs to be conducted longitudinally to the shell, but also needs to diffuse laterally between the cells to avoid local hotspots. This characteristic of graphene nanosheets just meets this requirement and is particularly suitable for uniform heat dissipation of high-energy-density batteries, reducing the problem of decreased battery consistency caused by uneven temperature distribution.

[0028] As a basic component of the flame retardant system, magnesium hydroxide works based on the principle of chemical endothermy. When the power battery experiences abnormally high temperatures, such as local overheating caused by a short circuit, a decomposition reaction occurs. The released water can absorb a large amount of heat, lowering the ambient temperature and slowing the spread of combustion. Compared to traditional high-filling flame retardant methods, the low proportion of magnesium hydroxide in this solution not only ensures the basic flame retardant effect, but also avoids the problems of reduced sealant flexibility and increased viscosity caused by high filling. This ensures that the sealant is not prone to cracking when the power battery undergoes vibration or temperature cycling, maintaining good interface sealing.

[0029] Expandable graphite acts as a physical barrier within the flame retardant system. It preferentially expands in the low-temperature range of 100–150°C, forming a fluffy carbon expansion layer. This structure effectively isolates oxygen and heat transfer, providing a first line of defense against the initial stages of thermal runaway in power batteries. In the initial stages of abnormal conditions such as battery overcharging, before the temperature rises dramatically, the rapid response of expandable graphite can suppress the spread of fire, buying time for subsequent flame retardant measures. Furthermore, the physical barrier formed by its expansion reduces heat transfer to adjacent cells, mitigating the risk of chain reactions.

[0030] The coated melamine polyphosphate / tannic acid intercalated nickel-aluminum hydrotalcite flame retardant is the core component of the flame retardant system, and its structural design enables it to work synergistically across different temperature ranges. The layered nickel-aluminum hydrotalcite undergoes dehydration and decarbonation reactions when heated, releasing inert gases and diluting the concentration of combustible gases. The intercalated structure of tannic acid and melamine polyphosphate can slow the decomposition rate of the flame retardant, extending its flame retardant duration and ensuring its effectiveness even during the sustained high-temperature phase of battery thermal runaway. The surface-coated polydimethylsiloxane not only reduces the interfacial tension between the flame retardant and the silicone rubber matrix, improving its dispersibility, but also forms a dense silicone protective layer at high temperatures, effectively suppressing molten dripping and preventing secondary combustion caused by molten dripping. The synergistic effect of this multi-layer structure provides a multi-level protection system of physical isolation, chemical inhibition, and thermal shielding in the open flame or sustained high-temperature environments that power batteries may face.

[0031] The polyphenolic hydroxyl groups of tannic acid are the core sites for its interfacial interaction. These hydroxyl groups can form hydrogen bonds with hydroxyl groups in silicone rubber molecular chains and enhance compatibility with the matrix through polar interactions. However, the phenolic hydroxyl groups of tannic acid are chemically sensitive. In acidic environments, the phenolic hydroxyl groups are easily protonated, reducing their polarity and hydrogen bonding ability with silicone rubber. In strongly alkaline environments, the phenolic hydroxyl groups dissociate into phenoloxy anions. Although their polarity is enhanced, they may over-coordinate with the metal ions of the nickel-aluminum hydrotalcite layers, locking the tannic acid between the layers and preventing it from effectively interacting with the silicone rubber, and even triggering oxidative degradation of the tannic acid. The design of a weakly alkaline intercalation environment precisely avoids both risks. This pH value neither protonates the phenolic hydroxyl groups of tannic acid nor causes them to over-dissociate, thereby maximizing the activity of the phenolic hydroxyl groups. At this time, the phenolic hydroxyl groups of tannic acid and the -OH groups in the silicone rubber molecular chain can form a dense hydrogen bond network. Each tannic acid molecule contains multiple phenolic hydroxyl groups, which can theoretically form multi-point hydrogen bonds with silicone rubber. This effect is much stronger than traditional physical adsorption and can effectively eliminate the interface gap between tannic acid as an intercalant and the silicone rubber matrix, thereby reducing thermal resistance.

[0032] After the weakly alkaline intercalation layer strengthens the interfacial bonding through hydrogen bonding, heat is smoothly transferred from the silicone rubber matrix to the nickel-aluminum hydrotalcite filler containing the tannic acid through the hydrogen-bonded network, where it then diffuses through the thermally conductive network. Power battery operating environments are subject to significant temperature fluctuations and vibration shock. Traditional sealants often experience interfacial delamination during temperature cycling due to weak interfacial bonding between the filler and the matrix, resulting in thermal conductivity degradation over time. However, the interfacial interaction between tannic acid and silicone rubber, formed through hydrogen bonding, exhibits a certain degree of dynamic adaptability. At low temperatures, hydrogen bonding is enhanced, inhibiting interfacial shrinkage; at high temperatures, hydrogen bonds moderately dissociate, alleviating thermal stress and preventing interfacial cracking. Furthermore, the weakly alkaline intercalation environment synergizes with the structural stability of the nickel-aluminum hydrotalcite. The layered structure of the nickel-aluminum hydrotalcite is more stable in weakly alkaline conditions, preventing premature disintegration of the nickel-aluminum hydrotalcite due to an inappropriate intercalation environment and ensuring targeted release of the tannic acid only when needed. It can be seen that in this application, tannic acid does not exist in a free state, but is embedded in the layered structure of nickel-aluminum hydrotalcite as an intercalant. This intercalation design allows the function of tannic acid to play a more precise and long-lasting role in the complex use scenarios of power battery sealants through interlayer constraints and controlled release mechanisms, while forming a synergistic effect with the flame retardant properties of nickel-aluminum hydrotalcite. Nickel-aluminum hydrotalcite has a typical layered stacking structure, and there is space between the layers to accommodate small molecules. The polyphenolic hydroxyl groups of tannic acid form a stable bond with the hydroxyl groups on the layer plates and the interlayer anions through hydrogen bonds. This intercalation state, on the one hand, avoids the early aggregation or oxidation failure of tannic acid due to direct exposure to the silicone rubber matrix, and on the other hand, achieves uniform dispersion of tannic acid. During the preparation process, this intercalation structure is further stabilized by hydrothermal reaction and surface coating to ensure that tannic acid is not released prematurely during processing links such as stirring and curing.

[0033] When microcracks develop in the sealant due to vehicle vibration or temperature cycling, stress concentration at the cracks triggers localized delamination of the nickel-aluminum hydrotalcite layered structure. This stress release weakens the interlaminar forces, allowing tannic acid molecules to migrate from the interlaminar structure to the crack interface, leveraging the polarity of the polyphenolic hydroxyl groups. At this point, the polyphenolic hydroxyl groups in the tannic acid rapidly form hydrogen bonds with the amino and hydroxyl groups in the silicone rubber molecular chains. Simultaneously, at temperatures between 60 and 80°C, this triggers the reversible breakage and recombination of dynamic phenol-carbamate bonds, reconnecting the molecular chains on either side of the crack through bond energy redistribution. This process is more targeted than free tannic acid: the intercalated structure allows the tannic acid to be released only at the onset of microcracks, avoiding the loss of repair efficiency caused by indiscriminate migration and reducing the risk of waterproofing failure or thermal runaway caused by microcrack propagation. The intercalated design also enhances the tannic acid's role as a crosslinker in enhancing tensile strength. The layered structure of nickel-aluminum hydrotalcite provides a nanoscale carrier for the dispersion of tannic acid. The intercalated tannic acid molecules are uniformly distributed within the sealant matrix through the constraints of the layers. Their polyphenolic hydroxyl groups form multi-point crosslinks with silicone rubber chains. The multiple phenolic hydroxyl groups on each tannic acid molecule can bind to the active sites of different silicone rubber chains, creating a three-dimensional network of crosslinks. This crosslinking method is more efficient than traditional small-molecule crosslinkers. The layers of nickel-aluminum hydrotalcite prevent the aggregation of tannic acid molecules, resulting in a more uniform distribution of crosslinking points, thereby achieving increased tensile strength at low addition levels.

[0034] At high temperature, the NiAl hydrotalcite decomposes to produce Ni 2+ As a Lewis acid catalyst, it can accelerate the aromatization and cross-linking reaction of tannic acid, greatly increasing the carbonization rate; at the same time, the phosphate groups released by the intercalated melamine polyphosphate at high temperature will undergo an esterification reaction with the polyphenolic hydroxyl groups of tannic acid to form a cross-linked structure containing phosphorus-carbon bonds. This structure not only enhances the density of the carbon layer, but also improves its antioxidant properties. Under the synergistic effect of the two, the carbon layer converted by tannic acid presents a dense and porous structure: the surface layer forms a dense shell due to the phosphate esterification of melamine polyphosphate, blocking oxygen and heat; the inner layer retains a certain amount of pores, and further reduces heat conduction through air insulation. This structure is just right for the high-temperature environment of power batteries during thermal runaway, and can effectively delay the transfer of heat to adjacent cells, avoiding the chain reaction of thermal runaway. The carbonization of traditional sealants mostly relies on a single carbon source such as graphite, but the graphite-based carbon layer is fluffy but has a loose structure and is easily oxidized and broken down at high temperatures; the carbon layer formed by tannic acid contains a phosphorus-carbon cross-linked structure and Ni 2+The graphitized microcrystals formed by catalysis have significantly improved high-temperature resistance and combine with inorganic oxides such as MgO and Al2O3 produced by the decomposition of nickel-aluminum hydrotalcite to form an "organic carbon-inorganic ceramic" composite carbon layer. This composite structure retains the flexibility of organic carbon and has the high-temperature resistance of inorganic ceramics. In addition, the carbonization process promoted by tannic acid can also reduce smoke release and toxic gas generation. The polyphenol structure of tannic acid mainly undergoes aromatization during carbonization, rather than violently decomposing to produce small molecular combustibles. Its carbonization reaction consumes some oxygen, reducing the generation rate of gases such as CO and CO2. It cooperates with the inert gases such as CO2 and NH3 released by nickel-aluminum hydrotalcite to further dilute the concentration of combustible gases, which can reduce the risk of suffocation caused by toxic smoke.

[0035] During the preparation process, the molecular weight and crosslink density of the base rubber are precisely controlled by controlling the amounts of water, tetramethylammonium hydroxide, tetraethyl orthosilicate, and dibutyltin dilaurate. The addition of water provides a reaction environment for the ring-opening polymerization of cyclosiloxanes. Tetramethylammonium hydroxide acts as a catalyst to accelerate the polymerization reaction. Tetraethyl orthosilicate acts as a crosslinker, reacting with the hydroxyl groups of the base rubber to form crosslinking points. Dibutyltin dilaurate promotes the uniformity of the crosslinking reaction through its catalytic effect. The resulting room-temperature paste-like vulcanized silicone rubber possesses both good flexibility to withstand the vibration conditions of power batteries and sufficient structural strength to ensure a good seal. Its viscosity also facilitates subsequent mixing with other components, ensuring a stable process.

[0036] Step S2: Mix expandable graphite with coated flame retardant and stir them in a high-speed mixer. The purpose of this operation is to break the agglomeration state of flame retardant particles through high-speed shear force, so that the two flame retardants form a uniform mixed system in advance, laying the foundation for subsequent mixing with the matrix. In the actual application of power battery sealant, the uniform dispersion of flame retardants is a prerequisite for ensuring the consistency of flame retardant effect. If it is unevenly dispersed, it may lead to insufficient local flame retardant performance and become a safety hazard. This step ensures the uniform distribution of flame retardant components in the matrix through mechanical force, thus avoiding this problem. Step S3: Add α-alumina and boron nitride to vulcanized silicone rubber, stir at high speed to form a heat-conducting matrix. The strong shear force generated by the high speed can evenly disperse the heat-conducting filler into the silicone rubber, ensuring the continuous construction of the heat-conducting path. In the use environment of the power battery, the sealant needs to be in contact with different materials such as the battery core and the shell. Good interface bonding not only improves the thermal conductivity efficiency, but also reduces the interface stress caused by thermal expansion and contraction, avoids cracking of the sealing layer, and ensures the thermal stability during long-term use.

[0037] Step S4 uses a gradient stirring strategy to sequentially add the flame retardant mixture, magnesium hydroxide, and graphene nanosheets to the heat-conducting matrix. The advantage of this stirring method is that the low-speed stage prevents the newly added components from splashing or agglomerating due to high-speed shearing, ensuring that the components are initially mixed evenly. The high-speed stage achieves deep dispersion of the components through strong shear forces, while also avoiding filler breakage problems that can occur with single high-speed stirring, such as the destruction of the graphene nanosheet layer structure. In the large-scale production of power battery sealants, this gradient stirring method can both ensure material uniformity and improve production efficiency, meet the production line's requirements for processing stability, and reduce product performance fluctuations caused by uneven mixing.

[0038] The vacuum degassing operation in step S5 is intended to remove bubbles introduced during the mixing process. The presence of bubbles can seriously affect the thermal conductivity and mechanical properties of the sealant. In the vibration or temperature cycling environment of the power battery, bubbles may expand and cause seal failure. Vacuum degassing ensures the sealant's internal structure is dense, improving its reliability in long-term use. The addition of dibutyltin dilaurate as a curing agent allows the cured sealant to form a stable cross-linked structure that can maintain elasticity and sealing in the temperature range of -40°C to 150°C that power batteries may face, resisting the stress shock caused by alternating hot and cold temperatures.

[0039] From the actual scenario of thermal runaway of power batteries, its temperature changes show obvious stage characteristics: the normal operating temperature is usually 25-60℃. When abnormalities such as short circuit and overcharging occur, the temperature will quickly rise to above 100℃, and then break through 150℃ to enter a period of intense reaction, and may eventually reach an extreme high temperature of more than 600℃. The gradient activation design is precisely aimed at this temperature process, allowing the flame retardant system to exert its force precisely at each critical stage. In the low temperature zone, the preferential expansion of expandable graphite is the first line of defense. The interlayers of expandable graphite contain intercalating agents. At 100-150℃, the intercalating agents are decomposed by heat to produce gas, which drives the graphite layer to quickly peel off and expand, forming a fluffy carbon layer with an expansion ratio of ≥100 times. The role of this expansion layer is dual: on the one hand, its porous structure can reduce the efficiency of heat conduction through the air insulation effect, delaying the transfer of heat from abnormal battery cells to adjacent battery cells. If the thermal runaway of a single battery cell cannot be curbed in time, it is very likely to cause the failure of the entire pack; on the other hand, the expansion layer can physically block the contact between oxygen and combustible materials, buying time for the battery management system to trigger emergency measures such as cooling and power off. When the temperature exceeds 150°C and enters the high-temperature zone, the expansion layer of the expandable graphite may experience structural collapse due to the continuous high temperature. At this time, the flame retardant mechanism is triggered to provide relay protection. The layered structure of nickel-aluminum hydrotalcite undergoes a violent dehydration and decarbonation reaction at a temperature greater than 150°C, and the layers disintegrate and release Ni²⁺ / Al³⁺ ions. These metal ions act as Lewis acid catalysts and can significantly accelerate the cross-linking reaction of silicone rubber molecular chains. The Si-OH groups in silicone rubber rapidly condense under the catalysis of Ni²⁺ / Al³⁺ to form a dense Si-O-Si three-dimensional network. This network not only improves the material's high-temperature resistance, but also locks in the carbonaceous components in the system, accelerates the hardening of the carbon layer, reduces the supply of combustibles to the flame zone, and suppresses the combustion intensity from the root.

[0040] From the perspective of the actual operational risks of power batteries, this gradient activation design can also address scenarios involving localized high-temperature breakthroughs. When a jet fire occurs in a battery pack cell due to an internal short circuit, the rapid expansion of expandable graphite before 150°C can initially block the lateral spread of the flame. The metal ions released by the flame retardant, catalyzed in the high-temperature zone, form a hard carbon layer that can withstand the direct burning of the jet fire, preventing the sealant from molten dripping and reducing secondary combustion caused by the molten droplets. Simultaneously, the formation of the hard carbon layer is accompanied by a large amount of inert gas, which further dilutes the oxygen concentration within the battery pack. Furthermore, this mechanism also meets the interfacial protection requirements of power battery sealants. The interface between the sealant and the cell and casing is a weak link in heat transfer and flame spread. The expansion of expandable graphite at 100-150°C fills interfacial gaps and enhances interfacial sealing. The Si-O-Si network formed by the flame retardant strengthens interfacial adhesion, preventing flames from penetrating through interfacial gaps. Conventional sealants often fail due to interfacial delamination at high temperatures, but this synergistic mechanism ensures the continuity of interfacial protection.

[0041] In summary, the beneficial effects of this application are:

[0042] 1. The matrix of this application uses vulcanized silicone rubber. Through precise cross-linking control, the viscosity is stabilized at 25,000-35,000 cps, taking into account both processing stability and sealing effect. It can closely fit the complex interface of the power battery, effectively blocking the intrusion of water and dust, and maintains elasticity in a wide temperature range of -40°C to 150°C, coping with vibration shock and temperature fluctuations, and solving the problem of high-temperature aging and cracking of traditional sealants.

[0043] 2. The α-alumina and boron nitride in the thermally conductive filler of this application construct a thermal conduction path to reduce the interfacial thermal resistance; the graphene nanosheets form a lateral thermal conductivity enhancement network to make up for the insufficient lateral heat transfer of a single filler, meet the needs of the power battery to conduct heat longitudinally to the shell and diffuse lateral heat to prevent hot spot accumulation, adapt to high energy density batteries to uniformly dissipate heat, and reduce the consistency drop caused by uneven temperature.

[0044] 3. In the flame retardant system of the present application, magnesium hydroxide cools down by chemical heat absorption, and a low filling amount takes into account both flame retardancy and flexibility; expandable graphite expands at low temperatures of 100-150°C to form a physical isolation layer, providing the first barrier for the early stage of thermal runaway; the coated flame retardant works synergistically in different temperature ranges to inhibit molten droplets and secondary combustion, adapting to the full stage protection of battery thermal runaway and reducing the risk of chain reactions.

[0045] 4. The tannic acid intercalation design in the flame retardant of this application retains the activity of phenolic hydroxyl groups in a weakly alkaline environment, forming strong hydrogen bonds with silicone rubber, eliminating interfacial gaps and reducing thermal resistance; dynamic hydrogen bonding can adapt to temperature cycles and vibrations, avoiding interfacial peeling; when microcracks occur, tannic acid is released in a directionally controlled manner, repairing the cracks through hydrogen bonds and reversible bonds, thereby improving long-term sealing and mechanical properties.

[0046] 5. This application adopts gradient stirring and other processes to ensure uniform dispersion of thermal conductive fillers and flame retardants to avoid local performance defects; vacuum degassing is used to remove bubbles to ensure a dense structure; the various components work together to avoid increased viscosity and decreased flexibility caused by high filling, ensuring that the sealant has stable performance during processing and use, and is adapted to large-scale production needs.

[0047] 6. The gradient activation design provided in this application matches the thermal runaway temperature stage. The expandable graphite blocks the spread of flames at an early stage, and the flame retardant in the high-temperature zone catalyzes the formation of a hard carbon layer to withstand burning, thereby strengthening interface protection and preventing flames from penetrating through gaps. It can cope with risks such as local high temperatures and jet fires, and improve the safety of battery packs. DETAILED DESCRIPTION

[0048] 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.

[0049] Example 1

[0050] Preparation of coated melamine polyphosphate / tannic acid intercalated nickel aluminum hydrotalcite flame retardant:

[0051] A. Take 10 g of layered nickel-aluminum hydrotalcite with a nickel-aluminum molar ratio of 2.5:1, add 100 mL of deionized water, then add 2.5 g of tannic acid, and ultrasonically disperse for 20 minutes. Adjust the pH of the system to 8.0 with aqueous ammonia, transfer the mixture to a reactor, and hydrothermally react at 80°C for 5 hours. After the reaction, filter, wash with deionized water until the filtrate is neutral, and vacuum dry at 80°C for 6 hours to obtain tannic acid-intercalated nickel-aluminum hydrotalcite.

[0052] B. Take 10 g of the tannic acid-intercalated nickel-aluminum hydrotalcite obtained in step A, add 5.56 g of melamine polyphosphate to 120 mL of deionized water, and stir at 45°C for 7 hours to carry out a hydrothermal intercalation reaction. After the reaction, filter and wash until the filtrate is free of impurities, and vacuum dry at 80°C for 6 hours to obtain melamine polyphosphate / tannic acid-intercalated nickel-aluminum hydrotalcite.

[0053] C. Prepare an 8 wt% polydimethylsiloxane ethyl acetate solution; take 10 g of the product obtained in step B and immerse it in the above solution for 1 hour; after taking it out, cure it at 75°C for 2 hours to form a polydimethylsiloxane surface coating; place the coated product in a vacuum oven, heat it at 110°C for 1.5 hours, then increase the temperature to 190°C and heat it for 0.5 hours, and cool it to obtain a coated melamine polyphosphate / tannic acid intercalated nickel aluminum hydrotalcite flame retardant.

[0054] Preparation of thermal conductive flame retardant dual-function power battery sealant:

[0055] S1. Take 100g of octamethylcyclotetrasiloxane, add 5g of deionized water and 0.1g of tetramethylammonium hydroxide, and react with stirring at 80°C under nitrogen for 4h to obtain α,ω-dihydroxypolydimethylsiloxane base rubber. Add 3g of ethyl orthosilicate and 0.5g of dibutyltin dilaurate to the base rubber and stir evenly to obtain a vulcanized silicone rubber that is in a paste form at room temperature.

[0056] S2. Take 1g of expandable graphite and 1g of the coated flame retardant obtained in step C, add them to a high-speed mixer, stir at 3000rpm for 20 minutes, and mix well for later use.

[0057] S3. Take 12g of α-alumina and 3g of boron nitride, add them to 100g of vulcanized silicone rubber obtained in step S1, and stir at 5000rpm for 30 minutes to form a thermally conductive matrix.

[0058] S4. To the thermally conductive substrate of step S3, the mixture obtained in step S2, 2 g of magnesium hydroxide, and 0.3 g of graphene nanosheets were added in sequence, and gradient stirring was adopted: first stirring at a low speed of 1000 rpm for 10 minutes, and then stirring at a high speed of 5000 rpm for 50 minutes to mix the components evenly.

[0059] S5. Place the mixture of step S4 in a vacuum degassing machine and degas at a vacuum degree of -0.08 MPa for 20 minutes; before use, add 1 g of curing agent dibutyltin dilaurate to the degassed mixture, stir evenly, and cure at 24°C for 1.5 hours to obtain a thermally conductive and flame-retardant dual-function power battery sealant.

[0060] Example 2

[0061] Preparation of coated melamine polyphosphate / tannic acid intercalated nickel aluminum hydrotalcite flame retardant:

[0062] A. Take 10 g of layered nickel-aluminum hydrotalcite with a nickel-aluminum molar ratio of 3:1, add 120 mL of deionized water, then add 2.8 g of tannic acid, and ultrasonically disperse for 25 minutes. Adjust the pH of the system to 8.2 with aqueous ammonia, transfer the system to a reactor, and hydrothermally react at 85°C for 5.5 hours. After the reaction, filter, wash with deionized water until the filtrate is neutral, and vacuum dry at 80°C for 6 hours to obtain tannic acid-intercalated nickel-aluminum hydrotalcite.

[0063] B. Take 10 g of the tannic acid-intercalated nickel-aluminum hydrotalcite obtained in step A, add 5 g of melamine polyphosphate to 110 mL of deionized water, and stir at 50°C for 7.5 hours to carry out a hydrothermal intercalation reaction. After the reaction, filter and wash until the filtrate is free of impurities, and vacuum dry at 80°C for 6 hours to obtain melamine polyphosphate / tannic acid-intercalated nickel-aluminum hydrotalcite.

[0064] C. Prepare a 9 wt% polydimethylsiloxane ethyl acetate solution; take 10 g of the product obtained in step B and immerse it in the above solution for 1.5 hours; after taking it out, cure it at 80°C for 2.5 hours to form a polydimethylsiloxane surface coating; place the coated product in a vacuum oven, heat it at 115°C for 2 hours, then increase the temperature to 195°C and heat it for 0.8 hours, and cool it to obtain a coated melamine polyphosphate / tannic acid intercalated nickel aluminum hydrotalcite flame retardant.

[0065] Preparation of thermal conductive flame retardant dual-function power battery sealant:

[0066] S1. Take 100g of octamethylcyclotetrasiloxane, add 5.5g of deionized water and 0.15g of tetramethylammonium hydroxide, and react at 82°C under nitrogen for 4.5h with stirring to obtain an α,ω-dihydroxypolydimethylsiloxane base rubber. Add 3.5g of ethyl orthosilicate and 0.6g of dibutyltin dilaurate to the base rubber and stir evenly to obtain a vulcanized silicone rubber that is a paste at room temperature.

[0067] S2. Take 1.5g of expandable graphite and 2g of the coated flame retardant obtained in step C, add them to a high-speed mixer, stir at 3200rpm for 22 minutes, and mix well for later use.

[0068] S3. Take 18g of α-alumina and 4.5g of boron nitride, add them to 100g of vulcanized silicone rubber obtained in step S1, and stir at 5200rpm for 32 minutes to form a thermally conductive matrix.

[0069] S4. To the thermally conductive substrate of step S3, the mixture obtained in step S2, 3g of magnesium hydroxide, and 0.5g of graphene nanosheets were added in sequence, and gradient stirring was adopted: first stirring at a low speed of 1200 rpm for 10 minutes, and then stirring at a high speed of 5200 rpm for 55 minutes to mix the components evenly.

[0070] S5. Place the mixture of step S4 in a vacuum degassing machine and degas at a vacuum degree of -0.085 MPa for 25 minutes; before use, add 1.5 g of curing agent dibutyltin dilaurate to the degassed mixture, stir evenly, and cure at 40°C for 6 hours to obtain a thermally conductive and flame-retardant dual-function power battery sealant.

[0071] Example 3

[0072] Preparation of coated melamine polyphosphate / tannic acid intercalated nickel aluminum hydrotalcite flame retardant:

[0073] A. Take 10 g of layered nickel-aluminum hydrotalcite with a nickel-aluminum molar ratio of 4:1, add 150 mL of deionized water, then add 3 g of tannic acid, and ultrasonically disperse for 30 minutes. Adjust the pH of the system to 8.5 with aqueous ammonia, transfer the mixture to a reactor, and hydrothermally react at 90°C for 6 hours. After the reaction, filter, wash with deionized water until the filtrate is neutral, and vacuum dry at 80°C for 6 hours to obtain tannic acid-intercalated nickel-aluminum hydrotalcite.

[0074] B. Take 10 g of the tannic acid-intercalated nickel-aluminum hydrotalcite obtained in step A, add 5 g of melamine polyphosphate to 150 mL of deionized water, and stir at 50°C for 8 h to carry out a hydrothermal intercalation reaction. After the reaction, filter and wash until the filtrate is free of impurities, and vacuum dry at 80°C for 6 h to obtain melamine polyphosphate / tannic acid-intercalated nickel-aluminum hydrotalcite.

[0075] C. Prepare a 10 wt% polydimethylsiloxane ethyl acetate solution; take 10 g of the product obtained in step B and immerse it in the above solution for 2 hours; after taking it out, cure it at 80°C for 3 hours to form a polydimethylsiloxane surface coating layer; place the coated product in a vacuum oven, heat it at 120°C for 2 hours, then increase the temperature to 200°C and heat it for 1 hour, and cool it to obtain a coated melamine polyphosphate / tannic acid intercalated nickel aluminum hydrotalcite flame retardant.

[0076] Preparation of thermal conductive flame retardant dual-function power battery sealant:

[0077] S1. Take 100g of octamethylcyclotetrasiloxane, add 6g of deionized water and 0.2g of tetramethylammonium hydroxide, and react at 85°C under nitrogen for 5h with stirring to obtain an α,ω-dihydroxypolydimethylsiloxane base rubber. Add 4g of ethyl orthosilicate and 0.8g of dibutyltin dilaurate to the base rubber and stir evenly to obtain a vulcanized silicone rubber that is a paste at room temperature.

[0078] S2. Take 2.5g of expandable graphite and 3g of the coated flame retardant obtained in step C, add them to a high-speed mixer, stir at 3500rpm for 25 minutes, and mix well for later use.

[0079] S3. Take 24g of α-alumina and 6g of boron nitride, add them to 100g of vulcanized silicone rubber obtained in step S1, and stir at 5500rpm for 35 minutes to form a thermally conductive matrix.

[0080] S4. To the thermally conductive substrate of step S3, the mixture obtained in step S2, 4 g of magnesium hydroxide, and 0.7 g of graphene nanosheets were added in sequence, and gradient stirring was adopted: first stirring at a low speed of 1500 rpm for 10 minutes, and then stirring at a high speed of 5500 rpm for 60 minutes to mix the components evenly.

[0081] S5. Place the mixture of step S4 in a vacuum degassing machine and degas at a vacuum degree of -0.09 MPa for 30 minutes; before use, add 2 g of curing agent dibutyltin dilaurate to the degassed mixture, stir evenly, and cure at 50°C for 10 hours to obtain a thermally conductive and flame-retardant dual-function power battery sealant.

[0082] Example 4

[0083] Preparation of coated melamine polyphosphate / tannic acid intercalated nickel aluminum hydrotalcite flame retardant:

[0084] A. Take 10 g of layered nickel-aluminum hydrotalcite with a nickel-aluminum molar ratio of 5:1, add 180 mL of deionized water, then add 3.2 g of tannic acid, and ultrasonically disperse for 35 minutes. Adjust the pH of the system to 8.8 with aqueous ammonia, transfer the system to a reactor, and hydrothermally react at 95°C for 6.5 hours. After the reaction, filter, wash with deionized water until the filtrate is neutral, and vacuum dry at 80°C for 6 hours to obtain tannic acid-intercalated nickel-aluminum hydrotalcite.

[0085] B. Take 10 g of the tannic acid-intercalated nickel-aluminum hydrotalcite obtained in step A, add 4.54 g of melamine polyphosphate to 130 mL of deionized water, and stir at 55°C for 8.5 hours to carry out a hydrothermal intercalation reaction. After the reaction, filter and wash until the filtrate is free of impurities, and vacuum dry at 80°C for 6 hours to obtain melamine polyphosphate / tannic acid-intercalated nickel-aluminum hydrotalcite.

[0086] C. Prepare an 11 wt% polydimethylsiloxane ethyl acetate solution; take 10 g of the product obtained in step B and immerse it in the above solution for 2.5 hours; after taking it out, cure it at 85°C for 3.5 hours to form a polydimethylsiloxane surface coating; place the coated product in a vacuum oven, heat it at 125°C for 2.5 hours, then increase the temperature to 205°C and heat it for 1.2 hours, and cool it to obtain a coated melamine polyphosphate / tannic acid intercalated nickel aluminum hydrotalcite flame retardant.

[0087] Preparation of thermal conductive flame retardant dual-function power battery sealant:

[0088] S1. Take 100g of octamethylcyclotetrasiloxane, add 7g of deionized water and 0.25g of tetramethylammonium hydroxide, and react at 88°C under nitrogen for 5.5h with stirring to obtain an α,ω-dihydroxypolydimethylsiloxane base rubber. 4.5g of ethyl orthosilicate and 0.9g of dibutyltin dilaurate are added to the base rubber and stirred evenly to obtain a vulcanized silicone rubber that is a paste at room temperature.

[0089] S2. Take 3g of expandable graphite and 3g of the coated flame retardant obtained in step C, add them to a high-speed mixer, stir at 3800rpm for 28 minutes, and mix well for standby.

[0090] S3. Take 30g of α-alumina and 5g of boron nitride, add them to 100g of vulcanized silicone rubber obtained in step S1, and stir at 5800rpm for 38 minutes to form a thermally conductive matrix.

[0091] S4. To the thermally conductive substrate of step S3, the mixture obtained in step S2, 5g of magnesium hydroxide, and 1.0g of graphene nanosheets were added in sequence, and gradient stirring was adopted: first stirring at a low speed of 1800 rpm for 10 minutes, and then stirring at a high speed of 5800 rpm for 65 minutes to mix the components evenly.

[0092] S5. Place the mixture of step S4 in a vacuum degassing machine and degas at a vacuum degree of -0.095 MPa for 35 minutes; before use, add 2.5 g of curing agent dibutyltin dilaurate to the degassed mixture, stir evenly, and cure at 70°C for 15 hours to obtain a thermally conductive and flame-retardant dual-function power battery sealant.

[0093] Example 5

[0094] Preparation of coated melamine polyphosphate / tannic acid intercalated nickel aluminum hydrotalcite flame retardant:

[0095] A. Take 10 g of layered nickel-aluminum hydrotalcite with a nickel-aluminum molar ratio of 15:1, add 200 mL of deionized water, then add 3.5 g of tannic acid, and ultrasonically disperse for 40 minutes. Adjust the pH of the system to 9.0 with aqueous ammonia, transfer the system to a reactor, and hydrothermally react at 100°C for 7 hours. After the reaction, filter, wash with deionized water until the filtrate is neutral, and vacuum dry at 80°C for 6 hours to obtain tannic acid-intercalated nickel-aluminum hydrotalcite.

[0096] B. Take 10 g of the tannic acid-intercalated nickel-aluminum hydrotalcite obtained in step A, add 4.54 g of melamine polyphosphate to 150 mL of deionized water, and stir at 55°C for 9 hours to carry out a hydrothermal intercalation reaction. After the reaction, filter and wash until the filtrate is free of impurities, and vacuum dry at 80°C for 6 hours to obtain melamine polyphosphate / tannic acid-intercalated nickel-aluminum hydrotalcite.

[0097] C. Prepare a 12 wt% polydimethylsiloxane ethyl acetate solution; take 10 g of the product obtained in step B and immerse it in the above solution for 3 hours; after taking it out, cure it at 85°C for 4 hours to form a polydimethylsiloxane surface coating; place the coated product in a vacuum oven, heat it at 130°C for 2.5 hours, then increase the temperature to 210°C and heat it for 1.5 hours, and cool it to obtain a coated melamine polyphosphate / tannic acid intercalated nickel aluminum hydrotalcite flame retardant.

[0098] Preparation of thermal conductive flame retardant dual-function power battery sealant:

[0099] S1. Take 100g of octamethylcyclotetrasiloxane, add 8g of deionized water and 0.3g of tetramethylammonium hydroxide, and react at 90°C under nitrogen for 6h with stirring to obtain an α,ω-dihydroxypolydimethylsiloxane base rubber. Add 5g of ethyl orthosilicate and 1g of dibutyltin dilaurate to the base rubber and stir evenly to obtain a vulcanized silicone rubber that is a paste at room temperature.

[0100] S2. Take 4g of expandable graphite and 4g of the coated flame retardant obtained in step C, add them to a high-speed mixer, stir at 4000rpm for 30 minutes, and mix well for standby.

[0101] S3. Take 33g of α-alumina and 11g of boron nitride, add them to 100g of vulcanized silicone rubber obtained in step S1, and stir at 6000rpm for 40 minutes to form a thermally conductive matrix.

[0102] S4. To the thermally conductive substrate of step S3, the mixture obtained in step S2, 6 g of magnesium hydroxide, and 1.2 g of graphene nanosheets were added in sequence, and gradient stirring was adopted: first stirring at a low speed of 2000 rpm for 10 minutes, and then stirring at a high speed of 6000 rpm for 80 minutes to mix the components evenly.

[0103] S5. Place the mixture of step S4 in a vacuum degassing machine and degas at a vacuum degree of -0.1 MPa for 40 minutes; before use, add 3g of curing agent dibutyltin dilaurate to the degassed mixture, stir evenly, and cure at 80°C for 24 hours to obtain a thermally conductive and flame-retardant dual-function power battery sealant.

[0104] Comparative Example 1 uses a "coated melamine polyphosphate intercalated nickel aluminum hydrotalcite flame retardant" that has not been intercalated with tannic acid to replace the coated flame retardant, and the rest is the same as Example 3.

[0105] In Comparative Example 2, the coated melamine polyphosphate / tannic acid intercalated nickel aluminum hydrotalcite flame retardant is not used, but is replaced by melamine polyphosphate of the same weight. Other aspects are the same as those of Example 3.

[0106] Comparative Example 3 removed the expandable graphite and replaced it with magnesium hydroxide of the same weight, and the rest was the same as Example 3.

[0107] Comparative Example 4 uses a "coated tannic acid intercalated nickel aluminum hydrotalcite flame retardant" that has not been intercalated with melamine polyphosphate to replace the coated flame retardant, and the rest is the same as Example 3.

[0108] In Comparative Example 5, the thermal conductive filler used was 15 g of α-alumina and 15 g of boron nitride, and the rest was the same as in Example 3.

[0109] In the preparation of the coated melamine polyphosphate / tannic acid intercalated nickel aluminum hydrotalcite flame retardant of Comparative Example 6, the pH of the system was not adjusted, and the rest was the same as in Example 3.

[0110] In the preparation of the coated melamine polyphosphate / tannic acid intercalated nickel aluminum hydrotalcite flame retardant in Comparative Example 7, hydrochloric acid was used to adjust the pH of the system to 4.5 in step A, and the rest was the same as in Example 3.

[0111] Comparative Example 8 does not use polydimethylsiloxane to coat the flame retardant, and the rest is the same as Example 3.

[0112] The above examples and comparative examples were subjected to performance tests using the following methods:

[0113] 1. The thermal conductivity coefficient is tested using the hot wire method. A sample with a thickness of 3 mm is tested and the thermal conductivity coefficient is calculated by applying a constant heating power and recording the temperature change.

[0114] 2. The flame retardant performance test adopts a vertical burning test. Place a 125mm×13mm×3mm sample vertically and burn it with a Bunsen burner for 10 seconds. Record the burning time and the droplet situation.

[0115] The limiting oxygen index tests the minimum oxygen concentration that can sustain combustion of a sample in an oxygen-nitrogen mixed flow;

[0116] Cone calorimeter was used to measure heat release rate, total heat release and smoke release.

[0117] 3. Tensile strength and elongation at break were measured using a universal material testing machine at a tensile speed of 50 mm / min.

[0118] 4. Aging test The samples were placed in an oven at 150 °C for 100 h, and the mass loss and changes in mechanical properties were measured.

[0119] 5. Viscosity test: Use a viscometer at 25°C and 20 rpm.

[0120] The test results of thermal conductivity, viscosity and tensile strength are shown in Table 1, the flame retardant properties are shown in Table 2, and the high temperature stability is shown in Table 3.

[0121] Table 1: Thermal conductivity and mechanical properties test results.

[0122]

[0123] Table 2: Flame retardant performance test results.

[0124]

[0125] Table 3: Performance test results of high temperature stability.

[0126]

[0127] Comparative Example 1 flame retardant has no tannic acid intercalation, and only retains nickel-aluminum hydrotalcite with melamine polyphosphate intercalation. Compared with Example 3, its thermal conductivity decreased by 31%. The reason is that the lack of tannic acid causes the flame retardant to lose the hydrogen bond network connection with the silicone rubber matrix, the interfacial thermal resistance increases significantly, and the originally continuous heat conduction path is interrupted. In terms of flame retardancy, the UL94 grade is reduced from V-0 to V-1, and the limiting oxygen index is reduced from 32% to 28%. This is because the polyphenolic hydroxyl groups without tannic acid are cross-linked with the silicone rubber molecular chain. The char layer formed at high temperature is loose and easily penetrated by flames, and a slight molten drop phenomenon occurs. In terms of mechanical properties, the tensile strength is reduced from 5.2MPa to 3.8MPa, and the elongation at break is reduced from 450% to 300%. This is mainly due to the weakening of the interfacial bonding force, which makes the material easily break at the interface between the flame retardant and the matrix when subjected to stress. High-temperature stability also deteriorated significantly. After aging at 150°C for 100 hours, the mass loss increased from 1.2% to 3.5%, and the tensile strength retention rate dropped from 92% to 65%. The lack of tannic acid failed to inhibit the high-temperature decomposition of the flame retardant, which accelerated the thermal oxidation aging of silicone rubber.

[0128] In Comparative Example 2, a single melamine polyphosphate replaces the coated flame retardant. Due to the strong polarity and poor dispersibility of melamine polyphosphate, its viscosity increases by 50% compared with Example 3. Due to the strong polarity and poor dispersibility of melamine polyphosphate, the high filling amount leads to increased friction in the system, seriously affecting the stirring and extrusion processing. The high filling amount leads to increased friction in the system, seriously affecting the stirring and extrusion processing. In terms of flame retardant properties, the heat release rate increases from 85kW / m² to 130kW / m². Since melamine polyphosphate has no layered structure and coating protection, it decomposes rapidly at high temperatures and cannot form a continuous and dense carbon layer. The heat release is more concentrated during combustion. In mechanical properties, the elongation at break drops from 450% to 330% because the high filling melamine polyphosphate destroys the flexibility of the silicone rubber molecular chain and increases the brittleness of the material.

[0129] Comparative Example 3: Removing expandable graphite and replacing it with an equal mass of magnesium hydroxide directly weakened the flame retardant barrier in the early stages of thermal runaway. Its UL94 rating dropped from V-0 to V-2. Due to the lack of the rapid expansion of expandable graphite at 100-150°C, a physical isolation layer could not be formed, allowing the flame to spread directly and obvious molten droplets to appear. The heat release rate surged from 85kW / m² to 150kW / m². Due to the loss of the initial oxygen and heat barrier, the combustion reaction became more intense, and a chain reaction was easily triggered when simulating battery thermal runaway. The thermal conductivity coefficient dropped from 1.6W / (m·K) to 1.1W / (m·K). Because the lamellar structure of expandable graphite originally helped to build the thermal conductivity network, the continuity of the path was reduced after its removal. After high-temperature aging, the excess magnesium hydroxide accelerated the rigidification of the silicone rubber molecular chain, making the material more brittle and hard.

[0130] The flame retardant in Comparative Example 4 lacks melamine polyphosphate intercalation, which destroys the tannic acid-melamine polyphosphate synergistic flame retardant mechanism. Its limiting oxygen index dropped from 32% to 29%. Because the phosphate groups released by melamine polyphosphate are not esterified with tannic acid at high temperatures, the carbon layer has a low crosslink density and poor oxidation resistance, making it difficult to block oxygen. The heat release rate increased from 85kW / m² to 115kW / m². Lacking the vapor-phase flame retardant and carbon layer-strengthening effects of melamine polyphosphate, the combustible gas concentration was higher and the combustion was more intense. After aging at 150°C, the tensile strength retention rate dropped from 92% to 80%. The lack of melamine polyphosphate reduced the stability of the nickel-aluminum hydrotalcite laminate, making it prone to disintegration at high temperatures and accelerating the aging of the substrate.

[0131] Comparative Example 5 exhibits an unbalanced ratio of thermally conductive fillers, causing its thermal conductivity to drop from 1.6 W / (m·K) to 1.0 W / (m·K). This is due to the excessive amount of small-particle boron nitride, which is unable to fill the gaps between the larger-particle α-alumina particles. Instead, nanoparticle agglomeration increases interfacial thermal resistance, disrupting the thermal path. Elongation at break drops from 450% to 350%. Excessive nanoparticles disrupt the flexibility of the silicone rubber's molecular chains, reducing the material's toughness and causing it to fracture brittlely when stretched. The heat release rate increases from 85 kW / m² to 110 kW / m². This poor thermal conductivity leads to heat concentration, accelerating the combustion reaction.

[0132] Comparative Example 6 failed to adjust the pH during tannic acid intercalation, disrupting the stability of the intercalated structure and increasing its viscosity from 30,000 cps to 38,000 cps. This is due to the partial protonation of the phenolic hydroxyl groups of the tannic acid in the weakly acidic environment, weakening the bond with the nickel-aluminum hydrotalcite layer. This weakened the flame retardant, increasing the viscosity of the system. Localized agglomeration and uneven dispersion of the flame retardant resulted in partial flame retardant failure, and the UL94 rating dropped from V-0 to V-1. Comparative Example 7 used hydrochloric acid to adjust the pH to 4.5 during intercalation, severely damaging the tannic acid activity and the nickel-aluminum hydrotalcite structure. Its tensile strength dropped from 5.2 MPa to 4.0 MPa. This is due to the complete protonation of the phenolic hydroxyl groups of the tannic acid in the strong acidic environment, which virtually eliminated hydrogen bonding with the silicone rubber and led to a sharp drop in interfacial bonding. After aging at 150°C, the mass loss increased from 1.2% to 2.6%. The acidic conditions caused the nickel-aluminum hydrotalcite layer to dissolve, prematurely decomposed the flame retardant, and accelerated thermal oxidative aging of the silicone rubber. Elongation at break dropped from 450% to 320%. Weak interfacial bonding made it easy to peel off from the flame retardant-matrix interface during stretching, significantly reducing ductility. Thermal conductivity dropped from 1.6W / (m·K) to 1.2W / (m·K). The dissolution of the laminate destroyed the flame retardant structure, making it unable to assist in building a thermal network, and the interfacial thermal resistance increased.

[0133] The surface of the flame retardant in Comparative Example 8 is not coated with polydimethylsiloxane, which weakens the interfacial compatibility and high-temperature stability. The interface between the flame retardant and the silicone rubber shows obvious peeling. The interfacial tension increases and the compatibility decreases due to the lack of PDMS. Obvious droplets appear during high-temperature combustion, while there are no droplets in Example 3. This is because the uncoated flame retardant lacks a silicone protective layer. After the decomposition of the nickel-aluminum hydrotalcite, the matrix easily melts and drips, causing secondary combustion. After aging at 150°C, the interfacial gap makes it easy for oxygen to invade, accelerating the breakage of the silicone rubber molecular chain, and the material becomes more hard and brittle. The heat release rate increases from 85kW / m² to 110kW / m². Although the droplets take away some heat, they trigger secondary combustion, and the overall heat release amount is higher.

Claims

1. A thermally conductive and flame-retardant dual-function power battery sealant, characterized in that: The following components are included in parts by mass: 100 parts of vulcanized silicone rubber, 15-45 parts of thermal conductive filler, 2-6 parts of magnesium hydroxide, 1-4 parts of expandable graphite, 1-4 parts of coated melamine polyphosphate / tannic acid intercalated nickel aluminum hydrotalcite flame retardant, and 0.3-1.2 parts of graphene nanosheets; The thermally conductive filler comprises 12-33 parts of α-alumina and 4-11 parts of boron nitride; The coated melamine polyphosphate / tannic acid intercalated nickel aluminum hydrotalcite flame retardant consists of a layered nickel aluminum hydrotalcite main body, an interlayer intercalant and a surface coating layer. The nickel-aluminum molar ratio of the layered nickel aluminum hydrotalcite is 15-2.5:1, the interlayer intercalant is tannic acid and melamine polyphosphate, and the surface coating layer is polydimethylsiloxane.

2. The thermally conductive and flame-retardant dual-function power battery sealant according to claim 1, characterized in that: In the thermally conductive filler, the mass ratio of α-alumina to boron nitride is 2-6:

1.

3. The thermally conductive and flame-retardant dual-function power battery sealant according to claim 1, characterized in that: The preparation method of the coated melamine polyphosphate / tannic acid intercalated nickel aluminum hydrotalcite flame retardant is as follows: A. Add nickel-aluminum hydrotalcite to deionized water at a solid-to-liquid ratio of 1:10-20, add tannic acid at a mass ratio of tannic acid to nickel-aluminum hydrotalcite of 2.5-3.5:10, and ultrasonically disperse for 20-40 minutes. Adjust the pH to 8.0-9.0 with aqueous ammonia. Transfer the mixture to a reactor and hydrothermally react at 80-100°C for 5-7 hours. Filter, wash, and dry to obtain tannic acid-intercalated nickel-aluminum hydrotalcite. B. Mixing the product obtained in step A with melamine polyphosphate in a mass ratio of 1.8-2.2:1 in deionized water at a solid-to-liquid ratio of 1:8-12, stirring at 45-55° C. for 7-9 hours, performing a hydrothermal intercalation reaction, filtering, washing, and drying to obtain a melamine polyphosphate / tannic acid intercalated nickel-aluminum hydrotalcite; C. The product obtained in step B is immersed in an ethyl acetate solution of 8-12 wt% polydimethylsiloxane for 1-3 hours, taken out and cured at 75-85°C for 2-4 hours to form a polydimethylsiloxane surface coating layer, and then placed in a vacuum oven, heated at 110-130°C for 1.5-2.5 hours, then heated to 190-210°C for 0.5-1.5 hours, and cooled to obtain a coated melamine polyphosphate / tannic acid intercalated nickel aluminum hydrotalcite flame retardant.

4. The thermally conductive and flame-retardant dual-function power battery sealant according to claim 1, characterized in that: The viscosity of the vulcanized silicone rubber is 25,000-35,000 cps, the particle size of the α-alumina is 5-50 μm, the particle size of the boron nitride is 50-200 nm, and the thickness of the graphene nanosheet is ≤5 nm.

5. A method for preparing the thermally conductive and flame-retardant dual-function power battery sealant according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1. Synthesis of vulcanized silicone rubber: Octamethylcyclotetrasiloxane was used as the raw material. Water and tetramethylammonium hydroxide catalyst were added. The mixture was stirred at 80-90°C under nitrogen for 4-6 hours to obtain an α,ω-dihydroxypolydimethylsiloxane base rubber. The base rubber was then mixed with tetraethyl orthosilicate and dibutyltin dilaurate and stirred to obtain a room temperature paste-like vulcanized silicone rubber. S2. The expandable graphite and coated melamine polyphosphate / tannic acid intercalated nickel aluminum hydrotalcite flame retardant mixed, added to a high-speed mixer 3000-4000rpm stirring for 20-30 minutes; S3. α-alumina and boron nitride are added to the vulcanized silicone rubber obtained in step S1 and stirred at 5000-6000 rpm for 30-40 minutes to form a thermally conductive matrix; S4. The mixture obtained in step S2, magnesium hydroxide, and graphene nanosheets are sequentially added to the thermally conductive substrate of step S3 and stirred for 1-1.5 hours; S5. Degas the mixture of step S4 under a vacuum degree of -0.08 to -0.1 MPa for 20-40 minutes, and add 1-3% of the mass of the mixture obtained in step S4 to cure it.

6. The method for preparing the thermally conductive and flame-retardant dual-function power battery sealant according to claim 5, characterized in that: In step S4, gradient stirring is adopted when adding each component: first stirring at a low speed of 1000-2000 rpm for 10 minutes, and then stirring at a high speed of 5000-6000 rpm for a total time of 1-1.5 hours.

7. The method for preparing the thermally conductive and flame-retardant dual-function power battery sealant according to claim 5, characterized in that: In step S5, the curing agent is dibutyltin dilaurate, the curing temperature is 24-80° C., and the curing time is 1.5-24 hours.

8. The method for preparing the thermally conductive and flame-retardant dual-function power battery sealant according to claim 5, characterized in that: In step S1, the amount of water added is 5%-8% of the mass of octamethylcyclotetrasiloxane, the amount of tetramethylammonium hydroxide added is 0.1%-0.3% of the mass of octamethylcyclotetrasiloxane, the amount of ethyl orthosilicate added is 3%-5% of the mass of octamethylcyclotetrasiloxane, and the amount of dibutyltin dilaurate added is 0.5%-1% of the mass of octamethylcyclotetrasiloxane.

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