CN120737801A

CN120737801A - Heat-conducting flame-retardant dual-functional power battery sealant and preparation method thereof

Info

Publication number: CN120737801A
Application number: CN202511251291.6A
Authority: CN
Inventors: 周福维; 董儒龙; 赵海英
Original assignee: Shandong Yuanteng New Material Technology Co ltd
Current assignee: Shandong Yuanteng New Material Technology Co ltd
Priority date: 2025-09-03
Filing date: 2025-09-03
Publication date: 2025-10-03

Abstract

The application belongs to the field of sealants, and particularly relates to a heat-conducting flame-retardant dual-function power battery sealant and a preparation method thereof. According to the application, the vulcanized silicone rubber is used as a matrix, the heat conduction system is formed by constructing a heat conduction path by alpha-alumina and boron nitride, and a transverse reinforced network is formed by matching with the graphene nanosheets, so that the interface thermal resistance is reduced, and the uniform diffusion of heat among the electric cores is realized. The flame-retardant system adopts expandable graphite, coated melamine polyphosphate/tannic acid intercalated nickel-aluminum hydrotalcite flame retardant and magnesium hydroxide. The preparation process adopts gradient stirring, vacuum defoaming and precise solidification control, and ensures uniform dispersion and structural densification of the components. The sealant disclosed by the application realizes the cooperative protection of physical isolation, chemical inhibition and heat shielding in the whole thermal runaway stage of the power battery, obviously reduces the local hot spot risk and the probability of chain reaction, improves the safety and prolongs the service life.

Description

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

Technical Field

The application belongs to the field of sealants, and particularly relates to a heat-conducting flame-retardant dual-function power battery sealant and a preparation method thereof.

Background

Under the background of rapid development of new energy automobile industry, the safety and reliability of the power battery are directly related to the performance of the whole automobile, while the sealant is used as a key material of a power battery packaging system, plays important roles of water resistance, dust resistance, vibration resistance, interface protection and the like, and has an irreplaceable role in long-term stable operation of the battery. Along with the continuous improvement of the energy density and the power density of the power battery, the heat generated in the working process of the power battery is obviously increased, and meanwhile, the complex electrochemical environment and the potential thermal runaway risk in the battery place more stringent requirements on the heat conduction performance and the flame retardant performance of the sealant.

In the charge-discharge cycle of the power battery, particularly under the high-rate working condition, a large amount of heat can be continuously generated, if the heat cannot be timely conducted to a heat dissipation system through the sealant, the local temperature of the battery is extremely easy to be overhigh, the aging of electrode materials and the decomposition of electrolyte can be accelerated, thermal runaway can be possibly caused, and potential safety hazards are caused. However, the heat conducting property of silicone rubber-based sealants widely used in the market at present is often difficult to meet the requirement of high-energy-density batteries. The sealant is mostly dependent on single or low-efficiency heat conducting fillers, and the heat conducting coefficient is generally lower than 1.0W/(m.K) due to uneven dispersion of the fillers or insufficient construction of a heat conducting passage, so that an efficient heat transfer path cannot be formed, and the increasing heat dissipation requirement of the power battery is difficult to deal with.

In addition to the heat conducting property, the flame retardant property is another key element of the power battery sealant for guaranteeing the safety. Under abnormal working conditions, the power battery may have short circuit, overcharge and other conditions, and local high temperature and even open flame are caused, and the sealant needs to have good flame retardant capability at the moment so as to delay the spread of fire and reduce the risk of thermal runaway. However, the existing sealant mostly adopts a single flame retardant such as magnesium hydroxide, the flame retardant can achieve basic flame retardant effect only through high filling amount, the mechanical properties such as flexibility, tensile strength and the like of the sealant can be obviously reduced through the high filling amount, so that the sealant is easy to crack in vibration or temperature circulation, the system viscosity can be greatly increased, the stability of the processing processes such as stirring and extrusion is influenced, meanwhile, the viscosity of the sealant can be obviously improved through the high filling amount, the uniform mixing is difficult in the stirring process, the deaeration is difficult, the defects such as bubbles and glue shortage are easy to occur in forming, the consistency of products is seriously influenced, the mass production is not facilitated, more importantly, the traditional flame retardant is easy to decompose and lose efficacy at high temperature, part of materials can even produce molten drop phenomenon, secondary combustion is possibly caused, and the requirement of a power battery on high-grade flame retardance is difficult to be met. Meanwhile, the temperature fluctuation of the working environment of the power battery is large, and in the long-term use process, the sealant needs to keep stable sealing performance at a high temperature. In the long-term use of the traditional silicone rubber-based sealant above 150 ℃, thermooxidative aging is easy to occur, molecular chain breakage and crosslinking density are reduced, the hardness of the material is increased, elasticity is lost, gaps are further caused at a sealing interface, impurities such as moisture, dust and the like cannot be effectively prevented from invading the inside of the battery, and the service life and the safety of the power battery are seriously influenced.

In summary, the current power battery sealant still faces many challenges in performance balance, the traditional product has insufficient heat conducting performance, cannot meet the heat dissipation requirement, sacrifices the mechanical property and processability of the material for pursuing the flame retardant effect, has poor stability in a high-temperature environment, and is difficult to reliably work for a long time.

Disclosure of Invention

In order to solve the problems, the application provides a heat-conducting flame-retardant dual-function power battery sealant and a preparation method thereof, wherein a vulcanized silicone rubber matrix and an alpha-alumina/boron nitride heat-conducting filler are cooperatively designed, and a tannic acid intercalation nickel-aluminum hydrotalcite flame retardant and a gradient activation flame-retardant system are combined to realize heat-conducting path construction and thermal runaway protection. The hydrogen bonding action of tannic acid and a matrix is enhanced through a weak alkaline environment, interface thermal resistance is eliminated, microcrack self-repairing capability is improved, meanwhile, a flame-retardant system forms a physical isolation layer in a low-temperature area, and a compact composite carbon layer is generated through catalysis in a high-temperature area, so that molten drops and secondary combustion are effectively inhibited. The preparation process ensures that the components are uniformly dispersed, and has low viscosity processability and high mechanical property, and elasticity is kept in a wide temperature range, so that the sealing reliability and thermal runaway safety of the power battery are obviously improved.

The application provides a heat-conducting flame-retardant dual-functional power battery sealant which comprises the following components in parts by weight:

100 parts of vulcanized silicone rubber, 15-45 parts of heat-conducting 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 nano sheet;

The heat conducting filler comprises 12-33 parts of alpha-alumina and 4-11 parts of boron nitride;

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

Further, in the heat conductive filler, the mass ratio of the alpha-alumina to the boron nitride is 2-6:1.

Furthermore, the preparation method of the coated melamine polyphosphate/tannic acid intercalated nickel aluminum hydrotalcite flame retardant comprises the following steps:

A. Adding deionized water into nickel aluminum hydrotalcite, wherein the solid-to-liquid ratio is 1:10-20, adding tannic acid, the mass ratio of tannic acid to nickel aluminum hydrotalcite is 2.5-3.5:10, performing ultrasonic dispersion for 20-40min, adjusting pH to 8.0-9.0 by ammonia water, transferring to a reaction kettle, performing hydrothermal reaction at 80-100 ℃ for 5-7h, filtering, washing and drying to obtain tannic acid intercalated nickel aluminum hydrotalcite;

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

C. And B, soaking the product obtained in the step B with ethyl acetate solution of 8-12wt% of polydimethylsiloxane for 1-3h, taking out, solidifying for 2-4h at 75-85 ℃ to form a polydimethylsiloxane surface coating layer, then placing in a vacuum oven, heating for 1.5-2.5h at 110-130 ℃, heating for 0.5-1.5h at 190-210 ℃, and cooling to obtain the coated melamine polyphosphate/tannic acid intercalated nickel aluminum hydrotalcite flame retardant.

Further, the viscosity of the vulcanized silicone rubber is 25000-35000cps, the particle size of the alpha-alumina is 5-50 mu m, the particle size of the boron nitride is 50-200nm, and the thickness of the graphene nano-sheet is less than or equal to 5nm.

The application also provides a preparation method of the heat-conducting flame-retardant dual-function power battery sealant, which comprises the following steps:

S1, synthesizing vulcanized silicone rubber, namely, octamethyl cyclotetrasiloxane is taken as a raw material, water and a tetramethylammonium hydroxide catalyst are added, stirring reaction is carried out for 4-6 hours at 80-90 ℃ under the protection of nitrogen, so as to obtain alpha, omega-dihydroxy polydimethylsiloxane base rubber, and the base rubber is mixed with tetraethoxysilane and dibutyltin dilaurate, and stirred to obtain pasty vulcanized silicone rubber at room temperature;

s2, mixing the expandable graphite with the coated melamine polyphosphate/tannic acid intercalated nickel aluminum hydrotalcite flame retardant, and adding the mixture into a high-speed mixer for stirring at 3000-4000rpm for 20-30 minutes;

S3, adding alpha-alumina and boron nitride into the vulcanized silicone rubber obtained in the step S1, and stirring at a high speed of 5000-6000rpm for 30-40 minutes to form a heat-conducting matrix;

s4, sequentially adding the mixture obtained in the step S2, magnesium hydroxide and graphene nano sheets into the heat-conducting substrate in the step S3, and stirring for 1-1.5 hours;

S5, defoaming the mixture obtained in the step S4 for 20-40 minutes under the vacuum degree of-0.08 to-0.1 MPa, and adding a curing agent accounting for 1-3% of the mass of the mixture obtained in the step S4 for curing.

Further, in the step S4, the components are added by adopting gradient stirring, namely, stirring for 10 minutes at a low speed of 1000-2000rpm and stirring for 1-1.5 hours at a high speed of 5000-6000 rpm.

Further, in step S5, the curing agent is dibutyltin dilaurate, the curing temperature is 24-80 ℃, and the curing time is 1.5-24 hours.

Further, in the step S1, the water addition amount is 5% -8% of the octamethyl cyclotetrasiloxane mass, the tetramethyl ammonium hydroxide addition amount is 0.1% -0.3% of the octamethyl cyclotetrasiloxane mass, the ethyl orthosilicate addition amount is 3% -5% of the octamethyl cyclotetrasiloxane mass, and the dibutyl tin dilaurate addition amount is 0.5% -1% of the octamethyl cyclotetrasiloxane mass.

The vulcanized silicone rubber is used as a matrix material of the sealant, plays a role in constructing an integral structure frame in a power battery packaging system, and has a molecular chain with specific flexibility and a three-dimensional network structure formed by crosslinking. In the preparation process, octamethyl cyclotetrasiloxane is used as a raw material, water and tetramethylammonium hydroxide are added as a catalyst to react under the protection of nitrogen to generate alpha, omega-dihydroxy polydimethylsiloxane base adhesive, then the alpha, omega-dihydroxy polydimethylsiloxane base adhesive is mixed with tetraethoxysilane and dibutyltin dilaurate, the tetraethoxysilane is used as a cross-linking agent to perform condensation reaction with the hydroxyl of the base adhesive, the dibutyltin dilaurate accelerates the cross-linking process through catalysis of the reaction, and the reaction is synergistic to form pasty vulcanized silicone rubber at room temperature, the viscosity of the vulcanized silicone rubber is controlled to 25000-35000cps, the viscosity range ensures the stability of stirring and extrusion in the processing process, avoids uneven mixing caused by flowing or overhigh viscosity, and can form a tightly attached sealing layer around a complex packaging interface of a power battery such as a clearance between a battery core and a shell and a pole, effectively prevent moisture and dust from invading, meanwhile, the problem that the traditional sealing adhesive is easy to crack at high temperature under aging due to vibration and impact of the vehicle running is solved.

The heat conducting filler consists of alpha-alumina and boron nitride in the mass ratio of 2-6:1. The alpha-alumina has the particle size of 5-50 mu m, belongs to large-particle-size filler, can construct a macroscopic heat conduction path in a matrix to provide a main channel for rapid heat transfer, and has the particle size of 50-200nm as small-particle-size filler to fill microscopic gaps among the large-particle-size alpha-alumina, so that interface obstruction in the heat transfer process is reduced, and the synergistic effect of the two obviously reduces interface thermal resistance. The introduction of the graphene nano sheet further strengthens the heat conduction performance of the sealant, the two-dimensional lamellar structure of the sealant can form a transverse heat conduction reinforcing network in the matrix, and the interaction between the lamellar layers and the hydrogen bond interaction of the silicon rubber molecular chain together form a continuous heat conduction path, so that the defect of the traditional single filler in transverse heat transfer is overcome. Inside power battery, the heat not only needs vertical conduction to the casing, still needs horizontal diffusion in order to avoid local hot spot gathering between the electric core, and this demand has been satisfied just to this characteristic of graphite alkene nanosheet, is particularly suitable for the even heat dissipation of high energy density battery, reduces the battery uniformity problem that leads to because of temperature distribution is uneven.

The magnesium hydroxide is used as a basic component of a flame-retardant system, and the action mechanism is based on a chemical heat absorption principle, so that when the power battery is subjected to abnormal high temperature such as local overheating caused by short circuit, decomposition reaction can occur, released water can absorb a large amount of heat, the temperature of the surrounding environment is reduced, and the combustion spreading speed is delayed. Compared with the traditional high-filling-amount flame-retardant mode, the low-fraction magnesium hydroxide in the scheme ensures the basic flame-retardant effect, avoids the problems of reduced flexibility and increased viscosity of the sealant caused by high filling, ensures that the sealant is not easy to crack when the power battery is subjected to vibration or temperature circulation, and maintains good interface tightness.

The expandable graphite plays a physical isolation role in a flame-retardant system, and can be expanded preferentially in a low-temperature region of 100-150 ℃ to form a fluffy carbonaceous expansion layer, so that the structure can effectively isolate oxygen from heat transfer, and a first protective barrier is provided for the initial thermal runaway stage of the power battery. In the initial stage of abnormal conditions such as battery overcharge, when the temperature has not risen sharply yet, the quick response of expandable graphite can in time restrain the development of fire, strives for time for the follow-up fire-retardant measure, and the physical barrier that its inflation formed can also reduce the transmission of heat to adjacent electric core simultaneously, reduces the chain reaction risk.

The coated melamine polyphosphate/tannic acid intercalated nickel aluminum hydrotalcite flame retardant is a core component of a flame retardant system, and the structural design of the flame retardant system enables the flame retardant to play a synergistic effect in different temperature ranges. The layered nickel aluminum hydrotalcite body is dehydrated and decarbonized to react when heated, inert gas is released to dilute the concentration of combustible gas, an intercalation structure of tannic acid and melamine polyphosphate can delay the decomposition rate of a flame retardant, prolong flame retardant aging, ensure that the flame retardant can still play a role in a continuous high-temperature stage of thermal runaway of a battery, and the surface-coated polydimethylsiloxane not only reduces the interfacial tension of the flame retardant and a silicone rubber matrix, improves dispersibility, forms a compact silicon-oxygen protective layer at high temperature, effectively inhibits the phenomenon of molten drops and avoids secondary combustion caused by the molten drops. The synergistic effect of this multi-layer structure creates a multi-level protection of physical isolation, chemical inhibition and thermal shielding in open fire or sustained high temperature environments that power cells may face.

The polyphenol hydroxyl groups of tannic acid are core sites which play an interface role, and the hydroxyl groups can form hydrogen bonds with hydroxyl groups in a silicon rubber molecular chain, and can enhance the compatibility with a matrix through polar interaction. However, phenolic hydroxyl groups of tannic acid are sensitive in chemical property, and are easy to protonate in an acidic environment, the polarity is weakened, the hydrogen bonding capability with silicon rubber is reduced, and in a strong alkaline environment, the phenolic hydroxyl groups are dissociated into phenolic oxyanions, and although the polarity is enhanced, the phenolic oxyanions can excessively coordinate with metal ions of a nickel aluminum hydrotalcite laminate, so that tannic acid is locked between layers and cannot form effective action with the silicon rubber, and even oxidative degradation of tannic acid is initiated. The design of the weak alkaline intercalation environment just avoids the two risks, and the pH value can not protonate the phenolic hydroxyl group of the tannic acid, can not cause excessive dissociation of the tannic acid, and maximally retains the activity of the phenolic hydroxyl group. At this time, the phenolic hydroxyl groups of tannic acid and-OH in the molecular chain of the silicone rubber can form a dense hydrogen bond network, each tannic acid molecule contains a plurality of phenolic hydroxyl groups, and theoretically, the tannic acid molecule can form a multi-point hydrogen bond effect with the silicone rubber, so that the effect is far stronger than the traditional physical adsorption, and the interface gap between tannic acid serving as an intercalation material and a silicone rubber matrix can be effectively eliminated, thereby reducing the thermal resistance.

After the weak alkaline intercalation is combined through a hydrogen bond strengthening interface, heat can be smoothly transferred from a silicon rubber matrix to nickel aluminum hydrotalcite filler where tannic acid is located through a hydrogen bond network, and then the heat is diffused through a heat conduction network. The working environment of the power battery has obvious temperature fluctuation and vibration impact, and the traditional sealant is often subjected to interface stripping in temperature circulation due to weak bonding force between the filler and the matrix interface, so that the heat conduction performance is attenuated along with the service time. The interface effect formed by the tannic acid and the silicon rubber through the hydrogen bond has certain dynamic adaptability, the hydrogen bond effect is enhanced at low temperature, interface shrinkage is restrained, the hydrogen bond is moderately dissociated at high temperature, thermal stress is relieved, and interface cracking is avoided. In addition, the weakly alkaline intercalation environment also forms a synergy with the structural stability of nickel aluminum hydrotalcite. The layered structure of the nickel-aluminum hydrotalcite is more stable under weak alkalinity, so that the nickel-aluminum hydrotalcite can be prevented from being disintegrated in advance due to improper intercalation environment, and the tannic acid is ensured to be directionally released when needed. Therefore, in the application, tannic acid does not exist in a free state, but is embedded into the layered structure of the nickel-aluminum hydrotalcite as an intercalation material, and the intercalation design enables the function of tannic acid to play a role more accurately and longer in a complex use scene of the power battery sealant through an interlayer constraint and controllable release mechanism, and simultaneously forms a synergistic effect with the flame retardant property of the nickel-aluminum hydrotalcite. The nickel aluminum hydrotalcite has a typical layered stacked structure, spaces capable of containing small molecules exist between layers, polyphenol hydroxyl groups of tannic acid form stable combination with hydroxyl groups on a laminate and interlayer anions through hydrogen bonds, and the intercalation state avoids early agglomeration or oxidation failure of tannic acid caused by direct exposure in a silicon rubber matrix on one hand, and realizes uniform dispersion of tannic acid on the other hand. In the preparation process, the intercalation structure is further stabilized with the surface coating layer through a hydrothermal reaction, so that tannic acid is ensured not to be released in advance in the processing links such as stirring, solidifying and the like.

When the sealant generates microcracks due to vehicle vibration or temperature circulation, stress concentration at the cracks can trigger local stripping of the nickel-aluminum hydrotalcite layered structure, interlayer acting force is weakened due to stress release, and tannic acid molecules migrate from the interlayer to the crack interface by virtue of the polarity of polyphenol hydroxyl groups. At this time, the polyphenol hydroxyl of tannic acid forms a hydrogen bond network with amino groups and hydroxyl groups in the molecular chains of the silicon rubber rapidly, and at the same time, the reversible fracture and recombination of the dynamic phenol-carbamate bonds are triggered at 60-80 ℃, and the molecular chains at two sides of the crack are reconnected through bond energy redistribution. Compared with free tannic acid, the intercalation structure enables tannic acid to be directionally released only when microcracks are generated, so that repair efficiency loss caused by indiscriminate migration is avoided, and the risk of waterproof failure or thermal runaway caused by microcrack expansion is reduced. Tannic acid acts as a cross-linking agent to increase tensile strength and is reinforced by intercalation design. The layered structure of nickel aluminum hydrotalcite provides nano-scale dispersed carrier for tannic acid, intercalated tannic acid molecules are uniformly distributed in a sealant matrix through laminate restraint, polyphenol hydroxyl groups of the tannic acid molecules can form multi-point crosslinking with silicon rubber molecular chains, and a plurality of phenolic hydroxyl groups of each tannic acid molecule can be combined with active sites of different silicon rubber molecular chains to construct a three-dimensional reticular crosslinking structure. Compared with the traditional small molecular cross-linking agent, the cross-linking mode is more efficient, and the laminate of the nickel-aluminum hydrotalcite blocks the aggregation of tannic acid molecules, so that the cross-linking points are distributed more uniformly, and the tensile strength is improved under the condition of low addition amount.

At high temperature, ni ²⁺ generated by decomposing nickel aluminum hydrotalcite is used as Lewis acid catalyst to accelerate aromatization and crosslinking reaction of tannic acid, greatly improving carbonization rate, and at the same time, the phosphate group released by the intercalated melamine polyphosphate at high temperature can generate esterification reaction with polyphenol hydroxyl of tannic acid to form a crosslinking structure containing phosphorus-carbon bond, which not only enhances the compactness of the carbon layer, but also improves oxidation resistance. Under the synergistic effect of the two, the tannic acid converted carbon layer presents a compact and porous structure, wherein a surface layer forms a compact shell layer for blocking oxygen and heat due to the phosphorylation of melamine polyphosphate, a certain pore is reserved in the inner layer, and the heat conduction is further reduced through air heat insulation. The carbonization of the traditional sealant is mostly dependent on a single carbon source such as graphite, but the graphite-based carbon layer is fluffy but loose in structure and is easy to oxidize and break down at high temperature, and the carbon layer formed by the promotion of tannic acid is obviously improved in high temperature resistance due to graphitized microcrystal formed by catalysis of a phosphorus-carbon-containing crosslinked structure and Ni ²⁺, and is combined with inorganic oxides such as MgO, al ₂O₃ and the like generated by the decomposition of nickel-aluminum hydrotalcite to form an organic carbon-inorganic ceramic composite carbon layer, so that the composite structure not only maintains the flexibility of the organic carbon, but also has the high temperature resistance of inorganic ceramics. In addition, the tannic acid-promoted carbonization process can also reduce smoke release and toxic gas generation. The polyphenol structure of tannic acid is mainly aromatized during carbonization, rather than violently decomposed to produce micromolecular combustible substances, and the carbonization reaction consumes part of oxygen, so that the generation rate of gases such as CO, CO ₂ and the like is reduced, and the polyphenol structure is cooperated with inert gases such as CO ₂、NH₃ and the like released by nickel aluminum hydrotalcite, so that the concentration of the combustible gas is further diluted, and the choking risk caused by toxic smoke can be reduced.

In the preparation step, the molecular weight and the crosslinking density of the base adhesive are accurately regulated and controlled by controlling the dosage of water, tetramethyl ammonium hydroxide, tetraethoxysilane and dibutyl tin dilaurate. The addition of water provides a reaction environment for ring-opening polymerization of cyclosiloxane, tetramethyl ammonium hydroxide is used as a catalyst to accelerate the polymerization reaction, tetraethoxysilane is used as a cross-linking agent to react with hydroxyl groups of base rubber to form cross-linking points, dibutyl tin dilaurate is used for promoting the uniform progress of the cross-linking reaction through catalysis, and finally the obtained room-temperature paste-like vulcanized silicone rubber has good flexibility to adapt to the vibration working condition of a power battery, has enough structural strength to ensure the sealing effect, and meanwhile, the viscosity characteristic of the room-temperature paste-like vulcanized silicone rubber is convenient for subsequent mixing with other components to ensure the stability of the processing process.

And S2, mixing the expandable graphite with the coated flame retardant and stirring in a high-speed mixer, wherein the aim of the operation is to break the aggregation state of the flame retardant particles through high-speed shearing force, so that the two flame retardants form a uniform mixed system in advance, and a foundation is laid for the subsequent mixing with a matrix. In the practical application of the power battery sealant, the uniform dispersion of the flame retardant is the premise of ensuring the consistency of the flame retardant effect, if the flame retardant is not uniformly dispersed, the partial flame retardant performance is possibly insufficient, and the flame retardant is a potential safety hazard, and the step ensures the uniform distribution of the flame retardant component in the matrix through the action of mechanical force, so that the problem is avoided. And S3, adding alpha-alumina and boron nitride into the vulcanized silicone rubber, stirring at a high speed to form a heat conduction matrix, and uniformly dispersing the heat conduction filler into the silicone rubber by using a strong shearing force generated by a high rotating speed to ensure continuous construction of a heat conduction path. In the service 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 combination not only improves heat conduction efficiency, but also reduces interface stress generated by thermal expansion and cold contraction, avoids cracking of a sealing layer, and ensures heat conduction stability in long-term use.

Step S4 adopts a gradient stirring strategy, and sequentially adds the flame retardant mixture, the magnesium hydroxide and the graphene nano-sheets into the heat conducting matrix, and the stirring mode has the advantages that the splashing or agglomeration of the just added components due to high-speed shearing can be avoided in a low-speed stage, the preliminary uniform mixing of the components is ensured, the deep dispersion of the components is realized through the high-speed stage by the high-shear force, and meanwhile, the problem of filler crushing possibly caused by single high-speed stirring, such as the damage to the lamellar structure of the graphene nano-sheets, is avoided. In the large-scale production of the power battery sealant, the gradient stirring mode can ensure the uniformity of materials, improve the production efficiency, adapt to the requirement of a production line on the processing stability, and reduce the fluctuation of the product performance caused by uneven mixing.

The vacuum defoaming operation in step S5 aims at removing bubbles introduced in the mixing process, the existence of the bubbles can seriously affect the heat conduction performance and mechanical properties of the sealant, and in the vibration or temperature cycle environment of the power battery, the bubbles can be expanded to cause sealing failure. The internal structure of the sealant is compact through vacuum defoamation, the reliability of the sealant in long-term use is improved, the dibutyl tin dilaurate is added as a curing agent, the cured sealant forms a stable cross-linked structure, the elasticity and the tightness can be kept in a temperature range of-40 ℃ to 150 ℃ which are possibly faced by a power battery, and the stress impact caused by alternating cold and hot is resisted.

From the practical scene of thermal runaway of the power battery, the temperature change of the power battery shows obvious stepwise characteristics that the normal working temperature is usually 25-60 ℃, when the abnormal conditions such as short circuit, overcharge and the like occur, the temperature can be quickly increased to be more than 100 ℃, then the temperature breaks through 150 ℃ to enter a severe reaction period, and finally the extremely high temperature of more than 600 ℃ can be possibly reached. The gradient activation design aims at the temperature process, so that the flame retardant system can accurately exert force at each key stage. In a low temperature region, the preferential expansion of the expandable graphite is a first defense line, an intercalation agent is contained between the layers of the expandable graphite, and at the temperature of 100-150 ℃, the intercalation agent is heated and decomposed to generate gas so as to promote the graphite layer to rapidly peel and expand, so that a fluffy carbonaceous layer with the expansion ratio of more than or equal to 100 times is formed. The expansion layer has the dual effects that on one hand, the porous structure can reduce heat conduction efficiency through the air heat insulation effect, delay heat transfer from an abnormal cell to an adjacent cell, and if the thermal runaway of a single cell can not be restrained in time, the whole cell is extremely easy to fail, on the other hand, the expansion layer can physically separate oxygen from contact with combustible materials, so that the time for triggering emergency measures such as cooling and power failure is striven for a battery management system. When the temperature breaks through 150 ℃ and enters a high temperature region, the expansion layer of the expandable graphite may collapse due to continuous high temperature, at the moment, the mechanism relay protection of the flame retardant is triggered, the layered structure of nickel aluminum hydrotalcite is subjected to severe dehydration decarbonation reaction at the temperature of more than 150 ℃, the laminate is disintegrated and releases Ni2+/Al3+ ions, the metal ions serve as Lewis acid catalysts, the crosslinking reaction of a molecular chain of the silicone rubber can be obviously accelerated, si-OH groups in the silicone rubber are rapidly condensed under the catalysis of Ni2+/Al3+ to form a compact Si-O-Si three-dimensional network, the network not only improves the high temperature resistance of the material, but also can lock the carbonaceous components in the system, accelerate the hardening of the carbon layer, reduce the supply of combustible materials to the flame region, and radically inhibit the combustion strength.

From the practical use risk of the power battery, the gradient activation design can also cope with the scene of local high-temperature breakthrough, when a certain cell of the battery pack generates injection fire due to internal short circuit, the rapid expansion of the expandable graphite before 150 ℃ can block the flame from spreading transversely, and the hard carbon layer formed by the catalysis of metal ions released by the flame retardant in a high-temperature area can bear the direct burning of the injection fire, so that the melting and dripping of the sealant are avoided, and the secondary combustion caused by the melting and dripping is reduced. At the same time, the formation of the hard carbon layer is accompanied by a large amount of inert gases that further dilute the oxygen concentration within the battery pack. In addition, the mechanism is also suitable for the interface protection requirement of the power battery sealant, the interface of the sealant, the battery core and the shell is a weak link of heat transfer and flame propagation, the expansion energy of the expandable graphite at 100-150 ℃ fills the interface gap to enhance the interface tightness, the Si-O-Si network formed by the flame retardant can strengthen the interface cohesive force to avoid the penetration of flame from the interface gap, the traditional sealant is peeled off at the interface at the height Wen Xiachang to cause flame retardant failure, and the cooperative mechanism ensures the continuity of interface protection.

In summary, the beneficial effects of the application are as follows:

1. The matrix of the application adopts the vulcanized silicone rubber, the viscosity is stabilized at 25000-35000cps through precise crosslinking control, the processing stability and the sealing effect are both considered, the complex interface of the power battery can be closely attached, the invasion of water dust is effectively prevented, the elasticity is kept in a wide temperature range from minus 40 ℃ to 150 ℃, the vibration impact and the temperature fluctuation are dealt with, and the problem of high-temperature aging cracking of the traditional sealant is solved.

2. The graphene nano sheets form a transverse heat conduction enhancement network, so that the defect of transverse heat transfer of a single filler is overcome, the requirements of longitudinal heat conduction to a shell and transverse diffusion hot spot aggregation prevention of a power battery are met, uniform heat dissipation of the high-energy-density battery is adapted, and consistency reduction caused by uneven temperature is reduced.

3. In the flame-retardant system, magnesium hydroxide is subjected to chemical heat absorption and temperature reduction, flame retardance and flexibility are both realized by low filling quantity, expandable graphite is expanded at a low temperature of 100-150 ℃ to form a physical isolation layer to provide a first barrier for the initial stage of thermal runaway, and a coated flame retardant is subjected to synergistic effect in different temperature ranges to inhibit molten drops and secondary combustion, so that the flame-retardant system is suitable for full-stage protection of thermal runaway of a battery and reduces the risk of chain reaction.

4. The tannic acid intercalation design in the flame retardant maintains phenolic hydroxyl activity through a weak alkaline environment, forms strong hydrogen bond action with silicon rubber, eliminates interface gaps, reduces thermal resistance, can adapt to temperature circulation and vibration, avoids interface stripping, directionally releases tannic acid when microcracks are generated, repairs the cracks through hydrogen bonds and reversible bonds, and improves long-term sealing performance and mechanical property.

5. The application adopts processes such as gradient stirring and the like to ensure that the heat conducting filler and the flame retardant are uniformly dispersed, avoid local performance defects, remove bubbles by vacuum defoamation, ensure compact structure, cooperatively avoid viscosity rise and flexibility reduction caused by high filling, ensure stable performance of the sealant in processing and use and adapt to the requirement of large-scale production.

6. The gradient activation design provided by the application is matched with a thermal runaway temperature stage, the expandable graphite can prevent flame from spreading in early stage, the flame retardant in a high temperature region is catalyzed to form a hard carbon layer to bear burning, interface protection is enhanced, flame penetration from gaps is avoided, risks of local high temperature, fire spraying and the like can be dealt with, and the safety of the battery pack is improved.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below. It will be apparent that the described embodiments are some, but not all, embodiments of the invention. All other embodiments, which are obtained by a person skilled in the art based on the described embodiments of the invention, fall within the scope of protection of the invention. It should be noted that the source of the raw materials not mentioned in the present invention may be commercially available or prepared by a conventional method, and the present invention is not limited thereto.

Example 1

Preparation of a coated melamine polyphosphate/tannic acid intercalated nickel aluminum hydrotalcite flame retardant:

A. Taking 10g of layered nickel aluminum hydrotalcite with the molar ratio of nickel to aluminum being 2.5:1, adding 100mL of deionized water, adding 2.5g of tannic acid, performing ultrasonic dispersion for 20min, adjusting the pH value of a system to 8.0 by using ammonia water, transferring to a reaction kettle, performing hydrothermal reaction at 80 ℃ for 5h, filtering after the reaction is finished, washing the filtrate to neutrality by using deionized water, and performing vacuum drying at 80 ℃ for 6h to obtain tannic acid intercalated nickel aluminum hydrotalcite.

B. And C, adding 10g of the tannic acid intercalated nickel-aluminum hydrotalcite obtained in the step A and 5.56g of melamine polyphosphate into 120mL of deionized water, stirring at 45 ℃ for 7h to perform hydrothermal intercalation reaction, filtering and washing until the filtrate is free of impurities after the reaction is finished, and drying at 80 ℃ in vacuum for 6h to obtain the melamine polyphosphate/tannic acid intercalated nickel-aluminum hydrotalcite.

C. preparing ethyl acetate solution of 8wt% polydimethylsiloxane, immersing 10g of the product obtained in the step B in the solution for 1h, taking out and solidifying at 75 ℃ for 2h to form a polydimethylsiloxane surface coating layer, placing the coated product in a vacuum oven, heating at 110 ℃ for 1.5h, heating to 190 ℃ for 0.5h, and cooling to obtain the coated melamine polyphosphate/tannic acid intercalated nickel-aluminum hydrotalcite flame retardant.

The preparation of the heat-conducting flame-retardant dual-function power battery sealant comprises the following steps:

S1, taking 100g of octamethyl cyclotetrasiloxane, adding 5g of deionized water and 0.1g of tetramethylammonium hydroxide, stirring and reacting for 4 hours at 80 ℃ under the protection of nitrogen to obtain alpha, omega-dihydroxy polydimethylsiloxane base rubber, adding 3g of tetraethoxysilane and 0.5g of dibutyltin dilaurate into the base rubber, and stirring uniformly to obtain pasty vulcanized silicone rubber at room temperature.

S2, 1g of expandable graphite and 1g of the coated flame retardant obtained in the step C are taken and added into a high-speed mixer, and are stirred for 20 minutes at 3000rpm, and are uniformly mixed for standby.

S3, adding 12g of alpha-alumina and 3g of boron nitride into 100g of vulcanized silicone rubber obtained in the step S1, and stirring at a high speed of 5000rpm for 30 minutes to form a heat conducting matrix.

S4, sequentially adding the mixture obtained in the step S2, 2g of magnesium hydroxide and 0.3g of graphene nano sheet into the heat conduction matrix in the step S3, and uniformly mixing the components by adopting gradient stirring, namely, firstly stirring at a low speed of 1000rpm for 10 minutes and then stirring at a high speed of 5000rpm for 50 minutes.

S5, placing the mixture obtained in the step S4 in a vacuum deaerating machine, deaerating for 20 minutes under the vacuum degree of minus 0.08MPa, adding 1g of curing agent dibutyl tin dilaurate into the deaerated mixture before use, uniformly stirring, and curing for 1.5 hours at 24 ℃ to obtain the heat-conducting flame-retardant dual-function power battery sealant.

Example 2

A. Taking 10g of layered nickel aluminum hydrotalcite with the molar ratio of nickel to aluminum being 3:1, adding 120mL of deionized water, adding 2.8g of tannic acid, performing ultrasonic dispersion for 25min, adjusting the pH value of a system to 8.2 by ammonia water, transferring to a reaction kettle, performing a hydrothermal reaction at 85 ℃ for 5.5h, filtering after the reaction is finished, washing the filtrate to neutrality by deionized water, and performing vacuum drying at 80 ℃ for 6h to obtain tannic acid intercalated nickel aluminum hydrotalcite.

B. And C, adding 10g of the tannic acid intercalated nickel-aluminum hydrotalcite obtained in the step A and 5g of melamine polyphosphate into 110mL of deionized water, stirring at 50 ℃ for 7.5h to perform hydrothermal intercalation reaction, filtering and washing until the filtrate is free of impurities after the reaction is finished, and drying at 80 ℃ in vacuum for 6h to obtain the melamine polyphosphate/tannic acid intercalated nickel-aluminum hydrotalcite.

C. Preparing ethyl acetate solution of 9wt% polydimethylsiloxane, immersing 10g of the product obtained in the step B in the solution for 1.5h, solidifying at 80 ℃ for 2.5h after taking out to form a polydimethylsiloxane surface coating layer, placing the coated product in a vacuum oven, heating at 115 ℃ for 2h, heating to 195 ℃ for 0.8h, and cooling to obtain the coated melamine polyphosphate/tannic acid intercalated nickel aluminum hydrotalcite flame retardant.

S1, taking 100g of octamethyl cyclotetrasiloxane, adding 5.5g of deionized water and 0.15g of tetramethylammonium hydroxide, stirring and reacting for 4.5 hours at 82 ℃ under the protection of nitrogen to obtain alpha, omega-dihydroxy polydimethylsiloxane base rubber, adding 3.5g of tetraethoxysilane and 0.6g of dibutyltin dilaurate into the base rubber, and stirring uniformly to obtain pasty vulcanized silicone rubber at room temperature.

S2, 1.5g of expandable graphite and 2g of the coated flame retardant obtained in the step C are taken and added into a high-speed mixer, and are stirred at 3200rpm for 22 minutes, and are uniformly mixed for standby.

S3, adding 18g of alpha-alumina and 4.5g of boron nitride into 100g of vulcanized silicone rubber obtained in the step S1, and stirring at a high speed of 5200rpm for 32 minutes to form a heat-conducting matrix.

S4, sequentially adding the mixture obtained in the step S2, 3g of magnesium hydroxide and 0.5g of graphene nano sheet into the heat conduction matrix in the step S3, and uniformly mixing the components by adopting gradient stirring, namely, firstly stirring at a low speed of 1200rpm for 10 minutes and then stirring at a high speed of 5200rpm for 55 minutes.

S5, placing the mixture obtained in the step S4 in a vacuum deaerating machine, deaerating for 25 minutes under the vacuum degree of minus 0.085MPa, adding 1.5g of curing agent dibutyl tin dilaurate into the deaerated mixture before use, uniformly stirring, and curing for 6 hours at 40 ℃ to obtain the heat-conducting flame-retardant dual-function power battery sealant.

Example 3

A. Taking 10g of layered nickel aluminum hydrotalcite with the molar ratio of nickel to aluminum being 4:1, adding 150mL of deionized water, adding 3g of tannic acid, performing ultrasonic dispersion for 30min, adjusting the pH value of a system to 8.5 by using ammonia water, transferring the system into a reaction kettle, performing a hydrothermal reaction at 90 ℃ for 6h, filtering after the reaction is finished, washing the solution to be neutral by using deionized water, and performing vacuum drying at 80 ℃ for 6h to obtain the tannic acid intercalated nickel aluminum hydrotalcite.

B. And C, adding 150mL of deionized water into 10g of the tannic acid intercalated nickel-aluminum hydrotalcite obtained in the step A and 5g of melamine polyphosphate, stirring for 8 hours at 50 ℃ to perform hydrothermal intercalation reaction, filtering and washing until the filtrate is free of impurities after the reaction is finished, and drying in vacuum at 80 ℃ for 6 hours to obtain the melamine polyphosphate/tannic acid intercalated nickel-aluminum hydrotalcite.

C. Preparing ethyl acetate solution of 10wt% polydimethylsiloxane, immersing 10g of the product obtained in the step B in the solution for 2 hours, taking out and solidifying at 80 ℃ for 3 hours to form a polydimethylsiloxane surface coating layer, placing the coated product in a vacuum oven, heating at 120 ℃ for 2 hours, heating to 200 ℃ for 1 hour, and cooling to obtain the coated melamine polyphosphate/tannic acid intercalated nickel-aluminum hydrotalcite flame retardant.

S1, taking 100g of octamethyl cyclotetrasiloxane, adding 6g of deionized water and 0.2g of tetramethylammonium hydroxide, stirring and reacting for 5 hours at 85 ℃ under the protection of nitrogen to obtain alpha, omega-dihydroxy polydimethylsiloxane base rubber, adding 4g of tetraethoxysilane and 0.8g of dibutyltin dilaurate into the base rubber, and stirring uniformly to obtain pasty vulcanized silicone rubber at room temperature.

S2, taking 2.5g of expandable graphite and 3g of the coated flame retardant obtained in the step C, adding the expandable graphite and the coated flame retardant into a high-speed mixer, stirring at 3500rpm for 25 minutes, and uniformly mixing for later use.

S3, adding 24g of alpha-alumina and 6g of boron nitride into 100g of vulcanized silicone rubber obtained in the step S1, and stirring at a high speed of 5500rpm for 35 minutes to form a heat-conducting matrix.

S4, sequentially adding the mixture obtained in the step S2, 4g of magnesium hydroxide and 0.7g of graphene nano sheet into the heat conduction matrix in the step S3, and uniformly mixing the components by adopting gradient stirring, namely, firstly stirring at a low speed of 1500rpm for 10 minutes and then stirring at a high speed of 5500rpm for 60 minutes.

S5, placing the mixture obtained in the step S4 in a vacuum deaerating machine, deaerating for 30 minutes under the vacuum degree of minus 0.09MPa, adding 2g of curing agent dibutyl tin dilaurate into the deaerated mixture before use, uniformly stirring, and curing for 10 hours at 50 ℃ to obtain the heat-conducting flame-retardant dual-function power battery sealant.

Example 4

A. Taking 10g of layered nickel aluminum hydrotalcite with the molar ratio of nickel to aluminum of 5:1, adding 180mL of deionized water, adding 3.2g of tannic acid, performing ultrasonic dispersion for 35min, adjusting the pH value of a system to 8.8 by using ammonia water, transferring to a reaction kettle, performing hydrothermal reaction at 95 ℃ for 6.5h, filtering after the reaction is finished, washing the filtrate to neutrality by using deionized water, and performing vacuum drying at 80 ℃ for 6h to obtain tannic acid intercalated nickel aluminum hydrotalcite.

B. And C, adding 130mL of deionized water into 10g of the tannic acid intercalated nickel-aluminum hydrotalcite obtained in the step A and 4.54g of melamine polyphosphate, stirring at 55 ℃ for 8.5h to perform hydrothermal intercalation reaction, filtering and washing until the filtrate is free of impurities after the reaction is finished, and vacuum drying at 80 ℃ for 6h to obtain the melamine polyphosphate/tannic acid intercalated nickel-aluminum hydrotalcite.

C. preparing an ethyl acetate solution of 11wt% polydimethylsiloxane, immersing 10g of the product obtained in the step B in the solution for 2.5 hours, solidifying at 85 ℃ for 3.5 hours after taking out to form a polydimethylsiloxane surface coating layer, placing the coated product in a vacuum oven, heating at 125 ℃ for 2.5 hours, heating to 205 ℃ for 1.2 hours, and cooling to obtain the coated melamine polyphosphate/tannic acid intercalated nickel aluminum hydrotalcite flame retardant.

S1, taking 100g of octamethyl cyclotetrasiloxane, adding 7g of deionized water and 0.25g of tetramethylammonium hydroxide, stirring and reacting for 5.5 hours at 88 ℃ under the protection of nitrogen to obtain alpha, omega-dihydroxy polydimethylsiloxane base rubber, adding 4.5g of tetraethoxysilane and 0.9g of dibutyltin dilaurate into the base rubber, and stirring uniformly to obtain pasty vulcanized silicone rubber at room temperature.

S2, taking 3g of expandable graphite and 3g of the coated flame retardant obtained in the step C, adding the materials into a high-speed mixer, stirring at 3800rpm for 28 minutes, and uniformly mixing for later use.

S3, adding 30g of alpha-alumina and 5g of boron nitride into 100g of vulcanized silicone rubber obtained in the step S1, and stirring at a high speed of 5800rpm for 38 minutes to form a heat-conducting matrix.

S4, sequentially adding the mixture obtained in the step S2, 5g of magnesium hydroxide and 1.0g of graphene nano sheet into the heat conduction matrix in the step S3, and uniformly mixing the components by adopting gradient stirring, namely, firstly stirring at a low speed of 1800rpm for 10 minutes and then stirring at a high speed of 5800rpm for 65 minutes.

S5, placing the mixture obtained in the step S4 in a vacuum deaerating machine, deaerating for 35 minutes under the vacuum degree of minus 0.095MPa, adding 2.5g of curing agent dibutyl tin dilaurate into the deaerated mixture before use, uniformly stirring, and curing for 15 hours at 70 ℃ to obtain the heat-conducting flame-retardant dual-function power battery sealant.

Example 5

A. Taking 10g of layered nickel aluminum hydrotalcite with the molar ratio of nickel to aluminum being 15:1, adding 200mL of deionized water, adding 3.5g of tannic acid, performing ultrasonic dispersion for 40min, adjusting the pH value of a system to 9.0 by using ammonia water, transferring to a reaction kettle, performing hydrothermal reaction at 100 ℃ for 7h, filtering after the reaction is finished, washing the filtrate to be neutral by using deionized water, and performing vacuum drying at 80 ℃ for 6h to obtain tannic acid intercalated nickel aluminum hydrotalcite.

B. And C, adding 10g of the tannic acid intercalated nickel-aluminum hydrotalcite obtained in the step A and 4.54g of melamine polyphosphate into 150mL of deionized water, stirring at 55 ℃ for 9h to perform hydrothermal intercalation reaction, filtering and washing until the filtrate is free of impurities after the reaction is finished, and drying at 80 ℃ in vacuum for 6h to obtain the melamine polyphosphate/tannic acid intercalated nickel-aluminum hydrotalcite.

C. preparing ethyl acetate solution of 12wt% polydimethylsiloxane, immersing 10g of the product obtained in the step B in the solution for 3 hours, solidifying at 85 ℃ for 4 hours after taking out to form a polydimethylsiloxane surface coating layer, heating the coated product in a vacuum oven at 130 ℃ for 2.5 hours, heating to 210 ℃ for 1.5 hours, and cooling to obtain the coated melamine polyphosphate/tannic acid intercalated nickel aluminum hydrotalcite flame retardant.

S1, taking 100g of octamethyl cyclotetrasiloxane, adding 8g of deionized water and 0.3g of tetramethylammonium hydroxide, stirring and reacting for 6 hours at 90 ℃ under the protection of nitrogen to obtain alpha, omega-dihydroxy polydimethylsiloxane base rubber, adding 5g of tetraethoxysilane and 1g of dibutyltin dilaurate into the base rubber, and stirring uniformly to obtain pasty vulcanized silicone rubber at room temperature.

S2, taking 4g of expandable graphite and 4g of the coated flame retardant obtained in the step C, adding the materials into a high-speed mixer, stirring at 4000rpm for 30 minutes, and uniformly mixing for later use.

S3, adding 33g of alpha-alumina and 11g of boron nitride into 100g of vulcanized silicone rubber obtained in the step S1, and stirring at a high speed of 6000rpm for 40 minutes to form a heat-conducting matrix.

S4, sequentially adding the mixture obtained in the step S2, 6g of magnesium hydroxide and 1.2g of graphene nano sheets into the heat conduction matrix in the step S3, and uniformly mixing the components by adopting gradient stirring, namely, firstly stirring at a low speed of 2000rpm for 10 minutes and then stirring at a high speed of 6000rpm for 80 minutes.

S5, placing the mixture obtained in the step S4 in a vacuum deaerating machine, deaerating for 40 minutes under the vacuum degree of minus 0.1MPa, adding 3g of curing agent dibutyl tin dilaurate into the deaerated mixture before use, uniformly stirring, and curing for 24 hours at 80 ℃ to obtain the heat-conducting flame-retardant dual-function power battery sealant.

Comparative example 1 the "coated melamine polyphosphate intercalated nickel aluminum hydrotalcite flame retardant" which had not undergone tannic acid intercalation was used instead of the coated flame retardant, and the remainder was the same as in example 3.

Comparative example 2 the same procedure as in example 3 was followed except that the coated melamine polyphosphate/tannin intercalated nickel aluminum hydrotalcite flame retardant was not used instead of the same weight of melamine polyphosphate.

Comparative example 3 the expandable graphite was removed, replaced with magnesium hydroxide of the same weight, and the rest was the same as in example 3.

Comparative example 4 the "coated tannic acid intercalated nickel aluminum hydrotalcite flame retardant" which had not been subjected to melamine polyphosphate intercalation was used instead of the coated flame retardant, and the remainder was the same as in example 3.

Comparative example 5 the heat conductive filler was 15g of alpha-alumina and 15g of boron nitride, and the remainder was the same as in example 3.

Comparative example 6 preparation of coated melamine polyphosphate/tannin intercalated nickel aluminum hydrotalcite flame retardant the pH of the system was not adjusted, and the rest was the same as in example 3.

Comparative example 7 preparation of coated melamine polyphosphate/tannin intercalated nickel aluminum hydrotalcite flame retardant the pH of the system was adjusted to 4.5 with hydrochloric acid in step a, the remainder being the same as in example 3.

Comparative example 8 the flame retardant was not coated with polydimethylsiloxane, and the remainder was the same as in example 3.

The performance test was performed on the above examples and comparative examples, and the test method is as follows:

1. Thermal conductivity test a sample 3mm thick was tested using the hot wire method and thermal conductivity was calculated by applying constant heating power and recording temperature changes.

2. The flame retardant performance test adopts a vertical burning test, a sample with the thickness of 125mm multiplied by 13mm multiplied by 3mm is vertically placed, a Bunsen burner is used for burning for 10 seconds, and the burning time and the molten drop condition are recorded;

limiting oxygen index the minimum oxygen concentration to maintain combustion of the sample was tested in an oxygen nitrogen mixed gas stream;

the cone calorimeter measures the rate of heat release, total heat release and smoke release.

3. The tensile strength and elongation at break were measured using a universal material tester at a tensile speed of 50mm/min.

4. Aging test samples were placed in a 150 ℃ oven for 100 hours to measure mass loss and mechanical property changes.

5. Viscosity testing was performed using a viscometer at 20rpm at 25 ℃.

The results of the heat conduction, viscosity and tensile strength performance tests are shown in Table 1, the flame retardant properties are shown in Table 2, and the high temperature stability is shown in Table 3.

Table 1 shows the results of heat conduction and mechanical property tests.

Table 2. Flame retardant property test results.

Table 3 shows the results of the performance test of the high temperature stability.

Comparative example 1 flame retardant was free of tannic acid intercalation and only melamine polyphosphate intercalated nickel aluminum hydrotalcite was retained. Compared with example 3, the heat conductivity coefficient of the flame retardant is reduced by 31 percent, because the loss of tannic acid causes the loss of hydrogen bond network connection between the flame retardant and the silicon rubber matrix, the interface thermal resistance is obviously increased, and the original continuous heat conduction path is interrupted. In terms of flame retardant properties, the UL94 rating is reduced from V-0 to V-1, and the limiting oxygen index is reduced from 32% to 28%, because no polyphenol hydroxyl groups of tannic acid are crosslinked with molecular chains of silicone rubber, a carbon layer formed at high temperature is loose and easy to break down by flame, and a slight molten drop phenomenon occurs. In mechanical property, the tensile strength is reduced from 5.2MPa to 3.8MPa, and the elongation at break is reduced from 450% to 300%, mainly because the interfacial binding force is weakened, and the material is easy to break from the interface of the flame retardant and the matrix when being stressed. The high-temperature stability is obviously deteriorated, the mass loss is increased from 1.2% to 3.5% and the tensile strength retention rate is reduced from 92% to 65% after the silicone rubber is aged for 100 hours at 150 ℃, and the high-temperature decomposition of the flame retardant cannot be inhibited due to the loss of tannic acid, so that the thermo-oxidative aging of the silicone rubber is accelerated.

Comparative example 2a single melamine polyphosphate replaces the coated flame retardant, and the viscosity of the flame retardant is increased by 50% compared with example 3 due to the strong polarity and poor dispersibility of the melamine polyphosphate, and the friction in the system is increased due to the strong polarity and poor dispersibility of the melamine polyphosphate, which seriously affects the stirring and extrusion processing. High loadings result in increased friction within the system, severely affecting stirring and extrusion processing. In the flame retardant property, the heat release rate is increased from 85kW/m < 2> to 130kW/m < 2>, and the melamine polyphosphate is free of a layered structure and is protected by a coating layer, so that the melamine polyphosphate is rapidly decomposed at high temperature, a continuous compact carbon layer cannot be formed, and the heat release is more concentrated during combustion. In the mechanical properties, the elongation at break is reduced from 450% to 330%, and the flexibility of the molecular chain of the silicone rubber is destroyed by the highly filled melamine polyphosphate, so that the brittleness of the material is increased.

Comparative example 3 removal of expandable graphite and replacement with equal mass magnesium hydroxide directly weakens the flame retardant barrier in the early stages of thermal runaway. The UL94 grade is reduced from V-0 to V-2, and a physical isolation layer cannot be formed due to the lack of the rapid expansion effect of the expandable graphite at 100-150 ℃, so that flame is easy to directly spread and obvious molten drops appear. The heat release rate is increased from 85kW/m < 2 > to 150kW/m < 2 >, and the combustion reaction is more severe due to the loss of the barrier between the initial oxygen and the heat, so that the chain reaction is extremely easy to be initiated when the thermal runaway of the battery is simulated. The heat conductivity coefficient is reduced from 1.6W/(m.K) to 1.1W/(m.K), and the continuity of the passage is reduced after removal because the lamellar structure of the expandable graphite originally assists in constructing a heat conducting network. After high-temperature aging, the rigidification of the silicon rubber molecular chain is accelerated by excessive magnesium hydroxide, and the material is more easy to rigidify and embrittle.

Comparative example 4 the flame retardant did not have melamine polyphosphate intercalation, disrupting the synergistic flame retardant mechanism of tannic acid-melamine polyphosphate. The limiting oxygen index is reduced from 32% to 29%, and the phosphoric acid group released by the melamine polyphosphate is not esterified with tannic acid at high temperature, so that the carbon layer has low crosslinking density and poor oxidation resistance, and is difficult to block oxygen. The heat release rate is increased from 85kW/m < 2 > to 115kW/m < 2 >, the gas phase flame retardance and carbon layer strengthening effect of the melamine polyphosphate are absent, the concentration of combustible gas is higher, and the combustion is more intense. After aging at 150 ℃, the retention rate of tensile strength is reduced from 92% to 80%, the stability of the nickel-aluminum hydrotalcite laminate is reduced due to the deficiency of melamine polyphosphate, the laminate is easy to disintegrate at high temperature, and the aging of a matrix is accelerated.

Comparative example 5 the thermal conductivity of the heat conductive filler was reduced from 1.6W/(m·k) to 1.0W/(m·k) due to the small-particle size boron nitride excess, the gaps of the large-particle size α -alumina could not be filled, but the interface thermal resistance was increased due to nanoparticle aggregation, and the thermal conductive path was broken. The elongation at break is reduced from 450% to 350%, the flexibility of the molecular chain of the silicone rubber is destroyed by excessive nano particles, the toughness of the material is reduced, and the material is easy to brittle fracture during stretching. The heat release rate is increased from 85kW/m <2 > to 110kW/m <2 >, and the heat is concentrated due to poor heat conduction, so that the combustion reaction is accelerated.

The comparative example 6 did not adjust pH during intercalation of tannic acid, and the stability of the intercalation structure was destroyed, the viscosity was increased from 30000cps to 38000cps, the binding force with nickel aluminum hydrotalcite laminate was weak, the flame retardant was easy to agglomerate, the system viscosity was increased, the local agglomeration and dispersion of the flame retardant was uneven, the UL94 grade was decreased from V-0 to V-1. Comparative example 7 the pH was adjusted to 4.5 with hydrochloric acid during intercalation, severely damaging tannic acid activity and nickel aluminium hydrotalcite structure. The tensile strength is reduced from 5.2MPa to 4.0MPa, the phenolic hydroxyl of tannic acid is completely protonated under strong acidity, the hydrogen bond action with the silicon rubber is almost eliminated, and the interface binding force is suddenly reduced. After 150 ℃ aging, the mass loss is increased from 1.2% to 2.6%, the nickel aluminum hydrotalcite laminate is dissolved under the acidic condition, the flame retardant is decomposed in advance, and the thermal oxidation aging of the silicon rubber is accelerated. The elongation at break is reduced from 450% to 320%, the interface bonding is weak, so that the adhesive is easy to peel from the interface between the flame retardant and the matrix during stretching, and the ductility is greatly reduced. The heat conductivity coefficient is reduced from 1.6W/(m.K) to 1.2W/(m.K), the laminate is dissolved to damage the flame retardant structure, a heat conduction network cannot be constructed in an auxiliary way, and the interface thermal resistance is increased.

Comparative example 8 the surface of the flame retardant was not coated with polydimethylsiloxane, impairing interfacial compatibility and high temperature stability. The flame retardant and the silicon rubber interface are obviously stripped, and the interfacial tension is increased and the compatibility is reduced due to the lack of PDMS. Obvious molten drops appear during high-temperature combustion, but in the embodiment 3, no molten drops exist, and the uncoated flame retardant lacks a silica protective layer, so that the matrix is easy to melt and drop after the nickel-aluminum hydrotalcite is decomposed, and secondary combustion is initiated. The interface gap is easy to invade oxygen after aging at 150 ℃, so that the molecular chain fracture of the silicon rubber is accelerated, and the material is more obvious in hard embrittlement. The heat release rate is increased from 85kW/m <2 > to 110kW/m <2 >, the molten drops take away part of heat but cause secondary combustion, and the total heat release amount is higher.

Claims

1. The heat-conducting flame-retardant dual-function power battery sealant is characterized by comprising the following components in parts by weight:

2. The thermally conductive flame retardant dual function power battery sealant of claim 1, wherein:

in the heat conducting filler, the mass ratio of the alpha-alumina to the boron nitride is 2-6:1.

3. The thermally conductive flame retardant dual function power battery sealant of claim 1, wherein:

The preparation method of the coated melamine polyphosphate/tannic acid intercalated nickel aluminum hydrotalcite flame retardant comprises the following steps:

4. The thermally conductive flame retardant dual function power battery sealant of claim 1, wherein:

The viscosity of the vulcanized silicone rubber is 25000-35000cps, the particle size of the alpha-alumina is 5-50 mu m, the particle size of the boron nitride is 50-200nm, and the thickness of the graphene nano sheet is less than or equal to 5nm.

5. A method for preparing the heat-conducting flame-retardant dual-function power battery sealant according to any one of claims 1-4, comprising the following steps:

6. The method for preparing the heat-conducting flame-retardant dual-function power battery sealant according to claim 5, which is characterized in that:

In the step S4, the components are added by adopting gradient stirring, namely, stirring for 10 minutes at a low speed of 1000-2000rpm and stirring for 1-1.5 hours at a high speed of 5000-6000 rpm.

7. The method for preparing the heat-conducting flame-retardant dual-function power battery sealant according to claim 5, which is characterized in that:

in the step S5, the curing agent is dibutyl tin dilaurate, the curing temperature is 24-80 ℃, and the curing time is 1.5-24 hours.

8. The method for preparing the heat-conducting flame-retardant dual-function power battery sealant according to claim 5, which is characterized in that:

The adding amount of water in the step S1 is 5-8% of the mass of the octamethyl cyclotetrasiloxane, the adding amount of tetramethyl ammonium hydroxide is 0.1-0.3% of the mass of the octamethyl cyclotetrasiloxane, the adding amount of tetraethoxysilane is 3-5% of the mass of the octamethyl cyclotetrasiloxane, and the adding amount of dibutyl tin dilaurate is 0.5-1% of the mass of the octamethyl cyclotetrasiloxane.