A high-temperature phase-change heat-insulating ceramic fiber aerogel and its preparation method

Abstract

The present invention belongs to the technical field of phase change ceramic fiber aerogels, and discloses a high-temperature phase change heat-insulating ceramic fiber aerogel and a preparation method thereof, including: adding polycarbosilane and polyvinylpyrrolidone into an organic solvent, mixing and stirring until completely dissolved to obtain a precursor solution; dispersing high-temperature phase change microcapsules into the precursor solution, stirring until uniformly dispersed to obtain a spinning solution; obtaining a ceramic precursor fiber membrane by electrospinning, and obtaining a high-temperature phase change heat-insulating ceramic fiber aerogel through crosslinking curing and sintering. The thermal conductivity of the high-temperature phase change heat-insulating ceramic fiber aerogel of the present invention can be adjusted between 0.03 and 0.05 W / (m·k), the phase change temperature is in the temperature range of 550 to 600 °C, and the phase change enthalpy value is 400 to 500 J / g. Compared with traditional ceramic aerogels, it can regulate the ambient temperature, is more heat-resistant and safer, and has wide applications in the field of high-temperature heat insulation for aviation power batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of phase change ceramic fiber aerogels, and particularly relates to a high-temperature phase change heat-insulating ceramic fiber aerogel and a preparation method thereof. Background Art

[0002] With the rapid development of electric aircraft, the aviation power battery system faces more stringent usage environments and performance requirements. In situations such as high-altitude flight and emergency acceleration of electric aircraft, power batteries are prone to serious safety hazards such as overheating and thermal runaway. Therefore, how to effectively manage the heat of aviation power batteries has become a key problem to be solved urgently.

[0003] Existing battery thermal management solutions mainly include: active cooling solutions such as liquid cooling and direct cooling technologies, and passive solutions such as phase change material heat absorption and heat pipe technologies. Among them, phase change materials have shown broad application prospects in the thermal management of aviation power batteries due to their unique advantage of absorbing a large amount of heat within the phase change temperature range. However, existing phase change materials still have the following deficiencies in practical applications: 1) The phase change temperature range cannot fully meet the requirements of aviation battery thermal management. The high temperature (>800°C) generated by thermal runaway of a single cell in an aviation power battery quickly spreads to the entire battery pack through heat conduction within 5 minutes. The high-temperature environment directly destroys the battery structure, accompanied by risks such as explosion, poisonous gas, and fire, making prevention and control extremely difficult. Currently, the phase change temperature of phase change materials is generally below 300°C, making it difficult to meet the prevention and control requirements for thermal runaway of aviation power batteries; 2) The structure of phase change materials is prone to damage at high temperatures, and problems such as leakage are likely to occur. Their mechanical strength and heat resistance are poor, and they cannot withstand extreme loads such as high temperature and vibration during battery use; 3) The integration of phase change materials with the battery thermal management system urgently needs to be improved. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the present invention provides a high-temperature phase change heat-insulating ceramic fiber aerogel and a preparation method thereof. Using high-strength and high-temperature-resistant ceramic fibers as the matrix, high-temperature phase change microcapsules are in-situ encapsulated. The prepared high-temperature phase change heat-insulating ceramic fiber aerogel can not only play the heat absorption function of the phase change material, but also enhance the reliability of the entire thermal management layer by virtue of the excellent mechanical and heat-resistant properties of the ceramic fibers. It can be directly integrated into the aviation power battery thermal management system, greatly improving the reliability of the battery in harsh environments such as high altitude, high temperature, and high vibration, and having wide applications in the field of aviation power battery thermal management.

[0005] The object of the present invention is achieved by the following technical solutions:

[0006] On the one hand, the present invention discloses a preparation method of a high-temperature phase change heat-insulating ceramic fiber aerogel, and the steps are as follows:

[0007] Step 1: Add polycarbosilane (PCS) and polyvinylpyrrolidone (PVP) into an organic solvent, mix and stir until completely dissolved to obtain a precursor solution;

[0008] Step 2: Disperse high-temperature phase change microcapsules into the precursor solution, stir until evenly dispersed to obtain a spinning solution;

[0009] Step 3: Electrospun the spinning solution to obtain a ceramic precursor fiber membrane containing high-temperature phase change microcapsules;

[0010] Step 4: Crosslink, cure and sinter the ceramic precursor fiber membrane to obtain a high-temperature phase change thermal insulation ceramic fiber aerogel.

[0011] Further, the organic solvent is one or more of N,N-dimethylformamide (DMF), tetrahydrofuran (THF), and isopropyl alcohol (IPA).

[0012] Further, in Step 1, the mass ratio of polycarbosilane (PCS) to polyvinylpyrrolidone (PVP) is (1-2):(1-2), and the ratio of the mass of polycarbosilane to the volume of the organic solvent is (1-2) g:(7-25) mL.

[0013] When too little polycarbosilane is added, after high-temperature sintering, the organic matter volatilizes, and polycarbosilane pyrolyzes at high temperature to form silicon carbide ceramics. Since the content of silicon carbide ceramics is low, after sintering, the fiber network does not have a good silicon carbide ceramic support skeleton, showing mechanical brittleness and fiber network collapse. When too much polycarbosilane is added, it will cause too many cross-linked structures to form inside the composite material, affecting the flexibility of the ceramic fiber. In addition, it will also cause stress concentration at the interface inside the fiber material, reducing the mechanical properties of the fiber material.

[0014] Polyvinylpyrrolidone, as a spinning aid in the spinning solution, when the content is too low, it seriously affects the spinning effect of the spinning solution, and there will be a solution spraying phenomenon, and no filamentous fibers appear on the receiver. When the content is too high, after the ceramic precursor fiber membrane is sintered, the organic matter (polyvinylpyrrolidone is the main organic matter) volatilizes, the ceramic fiber network collapses, the fibers are broken and damaged, showing a damaged fiber membrane phenomenon.

[0015] When too little organic solvent is added, during the dissolution process of polycarbosilane and polyvinylpyrrolidone, the dissolution is incomplete, and there will be agglomeration cross-linking and gelation phenomena, resulting in the failure of the precursor solution to dissolve. When too much organic solvent is added, the solution concentration is too low, which may damage the stretching and orientation of the polymer molecular chain, forming non-continuous fibers, showing a bead-like structure or broken filaments. In addition, the increase in the solvent content leads to a decrease in the solution viscosity, which weakens the stretching effect of the electric field on the jet, resulting in uneven fiber diameter distribution and reduced mechanical properties.

[0016] Further, the mixing and stirring time in Step 1 is 1 to 3 h.

[0017] Further, the average molecular weight of the polycarbosilane is 5000 - 8000 g / mol.

[0018] Further, the mass ratio of the polycarbosilane to the high-temperature phase change microcapsules is (1 - 2) : (2 - 10).

[0019] When the addition amount of the high-temperature phase change microcapsules is too low, the content of the phase change material in the fiber network decreases, seriously affecting the endothermic performance of the phase change ceramic fiber and reducing the overall heat insulation function of the ceramic fiber. When the addition amount of the high-temperature phase change microcapsules is too high, the silicon-aluminum alloy phase change microcapsules are stacked and there is adhesion in the fiber network, affecting the fiber network structure and causing a decrease in the mechanical properties of the fibers. In addition, adding too many phase change microcapsules will cause blockage of the needle during the electrospinning process, weakening the stretching effect of the electric field on the jet and resulting in uneven fiber diameter distribution.

[0020] Further, in Step 2, the high-temperature phase change microcapsules are silicon-aluminum alloy phase change microcapsules, the phase change temperature of the silicon-aluminum alloy phase change microcapsules is 550 - 600 °C, and the phase change enthalpy value is 400 - 500 J / g.

[0021] Further, the preparation method of the high-temperature phase change microcapsules in Step 2 is: impregnating micron-scale silicon-aluminum alloy powder in silica sol, heat-treating at 100 - 200 °C for 2 - 4 h to form a silica shell layer on the particle surface, and obtaining silica-coated silicon-aluminum alloy phase change microcapsules, where the mass ratio of the micron-scale silicon-aluminum alloy powder to the silica sol is 1 : 8 - 10.

[0022] Further, the process parameters of the electrospinning in Step 3 are: spinning voltage 8 - 18 kV, the distance between the spinneret and the receiving roller is 10 - 20 cm, the roller rotation speed is 150 - 300 rpm, and the syringe flow rate is 1 - 3 mL / h.

[0023] The spinning process of this application lies in that a spinning solution with polycarbosilane as the precursor, tetrahydrofuran as the organic solvent, and polyvinylpyrrolidone as the spinning aid, under the spinning voltage, receiving distance, and syringe flow rate, the prepared ceramic precursor fiber membrane has a complete structure, and after sintering, it exhibits good mechanical properties and heat insulation properties. Among the process parameters, the spinning voltage has a greater impact on the results of this application. When the spinning voltage is too high, the electric field force exceeds the surface tension of the polymer solution, resulting in the jet being over-stretched, which may cause fiber breakage or the formation of ultrafine fibers, destroying the stability of fiber deposition, resulting in rough fiber surfaces or holes. In addition, the high-intensity electric field causes the jet to accelerate and split during flight, forming multiple jets, resulting in chaotic distribution and serious adhesion of fibers on the collector. When the spinning voltage is insufficient, the electric field force cannot overcome the surface tension of the solution, resulting in the inability to form a Taylor cone for the droplets, only droplet ejection rather than continuous fibers. Under low voltage, the jet is insufficiently stretched, the fiber diameter increases significantly, and even an irregular film-like structure is formed. In addition, the insufficient electric field strength causes the jet velocity to slow down, the fiber production per unit time to decrease, and the collection distance needs to be shortened to maintain fiber formation, further restricting the process flexibility.

[0024] Further, in step 4, the temperature for crosslinking and curing is 150°C to 200°C, and the time is 1 to 2 h.

[0025] When the crosslinking and curing temperature is higher than 200°C, some polymers may undergo thermal decomposition or melting shrinkage at high temperatures, resulting in rough fiber surfaces and reduced porosity. Overheating may damage the orientation and crystallinity of polymer molecular chains, resulting in a decrease in the tensile strength and an increase in brittleness of the fiber membrane. The rapid volatilization of the solvent at high temperatures easily forms internal stress concentration, leading to cracking or delamination of the fiber membrane. When the crosslinking and curing temperature is lower than 150°C, the low temperature causes solvent residues, and the fibers are prone to adhesion, forming a dense film rather than a porous structure, reducing air permeability and specific surface area. The unevaporated solvent may corrode the fiber membrane, causing deformation or attenuation of mechanical properties after long-term storage. Some highly crystalline polymers are difficult to form a stable crystal structure at low temperatures, resulting in poor thermal stability of the fiber membrane.

[0026] Further, the sintering regime is: heating to 800°C to 1200°C at a heating rate of 5 °C / min in a nitrogen atmosphere and holding for 1 to 3 h.

[0027] When the heating temperature is lower than 800 °C, the precursor pyrolysis is insufficient at low temperature (such as <800 °C), and unreacted polymers or intermediate products remain, resulting in low fiber density and poor mechanical properties. The residual organic matter may reduce the oxidation resistance and high-temperature stability of ceramic fibers. In addition, the incompletely pyrolyzed ceramic precursor fibers may undergo secondary shrinkage or deformation during subsequent high-temperature applications. When the heating temperature is 1000 °C, the precursor pyrolyzes into amorphous or microcrystalline ceramics, which have good high-temperature resistance. At the same time, the phase change microcapsule structure is not damaged and is evenly distributed in the fiber aerogel. When the heating temperature is higher than 1200 °C, it causes excessive pyrolysis of the polymer precursor, accelerates atomic migration at high temperature, closes the pores inside the fiber, reduces the specific surface area and adsorption performance. In addition, when pyrolyzing at a temperature higher than 1200 °C, the fiber shrinkage rate is too high, which easily causes stress concentration, resulting in fiber fracture or surface cracking. The coarsening of grains (such as the grain size of β-SiC increasing from 50 nm to 200 nm) will weaken the high-temperature resistance of the fiber.

[0028] On the other hand, the present invention discloses a high-temperature phase change heat-insulating ceramic fiber aerogel prepared by the described preparation method. The ceramic fiber aerogel is a three-dimensional network structure in which high-temperature phase change microcapsules are in-situ encapsulated in a ceramic fiber network, and the thermal conductivity is 0.035~0.050 W·m -1 ·K -1 。

[0029] The present invention combines the precursor conversion method with the electrospinning process to in-situ encapsulate silicon-aluminum alloy phase change microcapsules into a ceramic fiber matrix, obtaining a high-temperature phase change heat-insulating ceramic fiber aerogel. The ceramic fiber has excellent mechanical strength, impact resistance and high-temperature resistance. Combined with high-temperature phase change microcapsules, it forms a gradient heat-insulating layer, and enhances the interfacial bonding strength through chemical cross-linking, which can maintain the structural integrity in an extremely high-temperature environment. When the temperature of the aviation power battery rises to the critical point, the phase change microcapsules absorb a large amount of heat. This in-situ phase change behavior can effectively inhibit the temperature rise rate and peak temperature of the aviation power battery, effectively delay the heating speed of the aviation power battery, provide a buffer time for the thermal runaway warning of the aviation power battery, and significantly improve the safety performance of the aviation power battery. The synergistic heat-insulating mechanism formed by the superposition of the low thermal conductivity of the ceramic fiber and the heat absorption characteristics of the phase change material significantly reduces the heat transfer rate to adjacent battery cells and improves the overall thermal management efficiency of the ceramic fiber aerogel.

[0030] The advantages and beneficial effects of the present invention are:

[0031] 1. Simple preparation process: During the preparation of fiber aerogel by uniaxial electrospinning, the high-temperature phase change microcapsules are dispersed in the spinning solution. During the electrospinning process, through process control, the phase change microcapsules are successfully distributed in the fiber aerogel network. The high-temperature phase change heat-insulating ceramic fiber aerogel can be successfully constructed by the simple uniaxial electrospinning technology. This preparation process is simple and fast, and can achieve efficient and large-scale production.

[0032] 2. Good heat-insulating performance: The high-temperature phase change heat-insulating ceramic fiber aerogel of the present invention has a low thermal conductivity (0.035 - 0.050 W·m -1 ·K -1 ), has good heat-insulating and thermal stability performance at high temperatures, can effectively block heat transfer, reduce thermal stress caused by temperature difference, and maintain the integrity and stability of the structure, and has broad application potential in the field of thermal management of aviation power batteries.

[0033] 3. High phase change endothermic temperature: For the high-temperature phase change heat-insulating ceramic fiber aerogel of the present invention, the phase change temperature range is: 550 - 600 °C, which can better meet the temperature requirements of thermal management of aviation power batteries. When the battery core gets out of control and generates high temperature (>800 °C), the phase change microcapsules absorb heat effectively, slow down the spread of high temperature, can resist thermal shock, enhance the service life of the fibers, can not only absorb a large amount of heat at critical temperatures, but also avoid the paralysis of the battery management system (BMS) caused by high-temperature heat conduction, the loss of voltage / temperature monitoring ability, and the phenomenon of accelerating the collapse of the whole system. This temperature matching is beneficial to improving the overall performance and reliability of the thermal management system. Description of the Drawings

[0034] Figure 1 is the preparation flow chart of the ceramic fiber aerogel of the present invention;

[0035] Figure 2 is the SEM image of the ceramic fiber aerogels prepared in Example 1, Example 3, Example 5, and Comparative Example 1 at a scale of 10 μm. Among them, a is the SEM image of the ceramic fiber aerogel prepared in Comparative Example 1, b is the SEM image of the ceramic fiber aerogel prepared in Example 1, c is the SEM image of the ceramic fiber aerogel prepared in Example 3, and d is the SEM image of the ceramic fiber aerogel prepared in Example 5;

[0036] Figure 3 is the SEM image of the ceramic fiber aerogel prepared in Example 3 at a scale of 300 μm;

[0037] Figure 4 is the XRD pattern of the ceramic fiber aerogels prepared in Example 3, Example 4, and Comparative Examples 2 - 4;

[0038] Figure 5 is the DSC pattern of the ceramic fiber aerogel prepared in Example 2.

[0039] Figure 6 The physical picture of the butane torch ablation of the ceramic fiber aerogel prepared in Example 3 and the infrared thermal imaging pictures of Example 1, Example 2, Example 3, Example 5, Comparative Example 1, and Comparative Example 6, where a is the physical picture of the butane torch ablation of the ceramic fiber aerogel prepared in Example 3, b is the front infrared thermal imaging picture of the ceramic fiber aerogel prepared in Example 3, c and d are the back infrared thermal imaging pictures of the ceramic fiber aerogel prepared in Example 3 after heating for 30 s and 120 s, respectively, e, f, g, and h are the back infrared thermal imaging pictures of the ceramic fiber aerogels prepared in Example 2, Example 1, Example 5, and Comparative Example 6 after heating for 120 s, respectively, and i is the back infrared thermal imaging picture of the ceramic fiber aerogel prepared in Comparative Example 1 after heating for 120 s. Detailed implementation manners

[0040] The present invention will be further described in detail below through specific examples. The following examples are only descriptive and not restrictive, and the protection scope of the present invention cannot be limited thereby.

[0041] Example 1

[0042] A preparation method of a high-temperature phase-change heat-insulating ceramic fiber aerogel, comprising:

[0043] (1) Take 2 g of polycarbosilane and 2.8 g of PVP, dissolve them in 12 mL of tetrahydrofuran, control the rotation speed at 300 rmp, and magnetically stir for 2 h to obtain a precursor solution;

[0044] (2) Take 2 g of silicon-aluminum alloy phase-change microcapsules, disperse and dissolve them in the precursor solution, control the rotation speed at 300 rmp, and magnetically stir for 1 h to obtain a spinning solution;

[0045] (3) Inject the obtained spinning solution into an electrospinning device, with a spinning voltage of 14 kV, a distance of 12 cm between the spinneret and the receiving roller, a roller rotation speed of 200 rpm, and a syringe flow rate of 3 mL / h to obtain a ceramic precursor fiber membrane;

[0046] (4) Place the ceramic precursor fiber membrane in a forced-air drying oven and thermally crosslink and cure it at 200 °C for 2 h, and then heat it to 1000 °C at a heating rate of 5 °C / min in a nitrogen atmosphere in a vacuum sintering furnace and sinter it for 2 h to obtain a high-temperature phase-change heat-insulating ceramic fiber aerogel.

[0047] Example 2

[0048] A preparation method of a high-temperature phase-change heat-insulating ceramic fiber aerogel, comprising:

[0049] (1) Take 2 g of polycarbosilane and 2.8 g of PVP, dissolve them in 12 mL of tetrahydrofuran, control the rotation speed at 300 rmp, and stir magnetically for 2 h to obtain a precursor solution;

[0050] (2) Take 5 g of silicon-aluminum alloy phase change microcapsules, disperse and dissolve them in the precursor solution, control the rotation speed at 300 rmp, and stir magnetically for 1 h to obtain a spinning solution;

[0051] (3) Inject the obtained spinning solution into an electrospinning device, with a spinning voltage of 14 kV, a distance of 12 cm between the spinneret and the receiving roller, a roller rotation speed of 200 rpm, and a syringe flow rate of 3 mL / h to obtain a ceramic precursor fiber membrane;

[0052] (4) Place the ceramic precursor fiber membrane in a forced-air drying oven and thermally crosslink and cure it at 200 °C for 2 h, then heat it to 1000 °C at a heating rate of 5 °C / min in a nitrogen atmosphere in a vacuum sintering furnace and sinter it for 2 h to obtain a high-temperature phase change heat-insulating ceramic fiber aerogel.

[0053] Example 3

[0054] A preparation method of a high-temperature phase change heat-insulating ceramic fiber aerogel, comprising:

[0055] (1) Take 2 g of polycarbosilane and 2.8 g of PVP, dissolve them in 12 mL of tetrahydrofuran, control the rotation speed at 300 rmp, and stir magnetically for 2 h to obtain a precursor solution;

[0056] (2) Take 10 g of silicon-aluminum alloy phase change microcapsules, disperse and dissolve them in the precursor solution, control the rotation speed at 300 rmp, and stir magnetically for 1 h to obtain a spinning solution;

[0057] (3) Inject the obtained spinning solution into an electrospinning device, with a spinning voltage of 14 kV, a distance of 12 cm between the spinneret and the receiving roller, a roller rotation speed of 200 rpm, and a syringe flow rate of 3 ml / h to obtain a ceramic precursor fiber membrane;

[0058] (4) Place the ceramic precursor fiber membrane in a forced-air drying oven and thermally crosslink and cure it at 200 °C for 2 h, then heat it to 1000 °C at a heating rate of 5 °C / min in a nitrogen atmosphere in a vacuum sintering furnace and sinter it for 2 h to obtain a high-temperature phase change heat-insulating ceramic fiber aerogel.

[0059] Example 4

[0060] The difference from Example 3 is only that the sintering temperature in step (4) is 800 °C.

[0061] Example 5

[0062] The difference from Example 3 is only that in step (2), 20 g of silicon-aluminum alloy phase change microcapsules are taken, dispersed and dissolved in the precursor solution, the rotation speed is controlled at 300 rmp, and magnetic stirring is carried out for 1 h to obtain a spinning solution.

[0063] Comparative Example 1

[0064] The preparation method is the same as that of Example 3, and the difference is only that silicon-aluminum alloy phase change microcapsules are not added.

[0065] Comparative Example 2

[0066] The preparation method is the same as that of Example 3, and the difference is only that in step (4), the sintering temperature is 600 °C.

[0067] Comparative Example 3

[0068] The preparation method is the same as that of Example 3, and the difference is only that in step (4), the sintering temperature is 750 °C.

[0069] Comparative Example 4

[0070] The preparation method is the same as that of Example 3, and the difference is only that in step (4), the sintering temperature is 1250 °C.

[0071] Comparative Example 5

[0072] The preparation method is the same as that of Example 3, and the difference is only in steps (1) and (2). 2 g of polycarbosilane, 2.8 g of PVP, and 5 g of silicon-aluminum alloy phase change microcapsules are dissolved in 12 mL of tetrahydrofuran, the rotation speed is controlled at 300 rmp, and magnetic stirring is carried out for 2 h to obtain a spinning solution.

[0073] Comparative Example 6 (preparation of high-temperature phase change thermal insulation ceramic fiber aerogel by vacuum impregnation of phase change microcapsules)

[0074] A preparation method of a high-temperature phase change thermal insulation ceramic fiber aerogel, comprising:

[0075] (1) Take 2 g of polycarbosilane and 2.8 g of PVP, dissolve them in 12 mL of tetrahydrofuran, control the rotation speed at 300 rmp, and carry out magnetic stirring for 2 h to obtain a precursor spinning solution;

[0076] (2) Inject the obtained precursor spinning solution into an electrospinning device, with a spinning voltage of 14 kV, a distance of 12 cm between the spinneret and the receiving roller, a roller rotation speed of 200 rpm, and a syringe flow rate of 3 ml / h to obtain a ceramic precursor fiber membrane;

[0077] (3) Place the ceramic precursor fiber membrane in a forced-air drying oven and thermally crosslink and cure it at 200 °C for 2 h. Then, heat it to 1000 °C at a heating rate of 5 °C / min in a nitrogen atmosphere in a vacuum sintering furnace and sinter it for 2 h to obtain a ceramic fiber aerogel with high-temperature heat insulation.

[0078] (4) Immerse the obtained ceramic fiber aerogel in an ethanol solution in which silicon-aluminum alloy phase change microcapsules are dispersed, and vacuum dry it at 60 °C for 2 h to obtain a high-temperature phase change heat insulation ceramic fiber aerogel composite with phase change microcapsules.

[0079] Performance testing and result analysis:

[0080] Place the high-temperature phase change heat insulation ceramic fiber aerogel prepared in the examples and comparative examples flat on the upper and lower surfaces of the sensor of a thermal conductivity tester (TC3000E, XIA TECH, CHN) to measure the thermal conductivity of the high-temperature phase change heat insulation ceramic fiber aerogel. The data are shown in Table 1.

[0081] Table 1 Performance test data of the high-temperature phase change heat insulation ceramic fiber aerogel prepared in the examples and comparative examples

[0082]

[0083] It can be clearly seen from the data in Table 1 that from Example 1 to Example 5, as the content of the silicon-aluminum alloy phase change microcapsules increases, the thermal conductivity of the high-temperature phase change thermal insulation ceramic fiber aerogel first decreases and then increases. This is because as the content of the silicon-aluminum alloy phase change microcapsules increases, the phase change microcapsules absorb heat when heat passes through the phase change ceramic fiber aerogel, reducing the heat conduction of the high-temperature phase change thermal insulation ceramic fiber aerogel. When the mass ratio of polycarbosilane to silicon-aluminum alloy phase change microcapsules in Example 3 is 1:5, the thermal insulation effect of the prepared phase change ceramic fiber aerogel is the best. When the content of the silicon-aluminum alloy phase change microcapsules continues to increase (Example 5), the silicon-aluminum alloy phase change microcapsules stack up and there is adhesion in the fiber network, affecting the fiber network structure and causing the thermal conductivity to increase and the thermal insulation effect to deteriorate. All the examples show better thermal insulation effects than the ceramic fiber aerogel of Comparative Example 1 without silicon-aluminum alloy microcapsules. Through thermal conductivity tests, it is found that compared with Comparative Example 1, adding silicon-aluminum alloy phase change microcapsules in Examples 1-5 reduces the thermal conductivity of the ceramic fiber aerogel and improves the thermal insulation effect of the ceramic fiber aerogel. In Comparative Example 5, polycarbosilane, PVP, and silicon-aluminum alloy phase change microcapsules are dissolved in tetrahydrofuran together, and the prepared ceramic fiber aerogel has poor thermal conductivity. This is because the main chain of the polycarbosilane molecule contains Si-C bonds and has a certain polarity, but its overall structure is still mainly composed of non-polar alkyl chains. Directly placing it in tetrahydrofuran will cause insufficient dissolution, and the polycarbosilane molecules will agglomerate and crosslink, resulting in uneven internal structure of the ceramic fiber aerogel and thus reducing the thermal insulation performance. In Comparative Example 6, the ceramic fiber aerogel prepared by the vacuum impregnation method has poor thermal conductivity. This is because when impregnating the phase change microcapsules in a vacuum environment, there is only a physical connection force between the ceramic matrix and the microcapsules. During the test, the microcapsules will fall off, reducing the heat storage density and temperature regulation ability of the ceramic fiber, affecting its thermal stability and energy efficiency. In addition, the falling off of the microcapsules will damage the composite structure of the ceramic fiber and reduce its overall mechanical strength.

[0084] The morphologies of the samples prepared in Example 1, Example 3, Example 5, and Comparative Example 1 were analyzed using a JSM-7800F field emission scanning electron microscope, as Figure 2 shown, where a is the SEM image of the ceramic fiber aerogel prepared in Comparative Example 1, b is the SEM image of the ceramic fiber aerogel prepared in Example 1, c is the SEM image of the ceramic fiber aerogel prepared in Example 3, and d is the SEM image of the ceramic fiber aerogel prepared in Example 5. From Figure 2It can be seen from c (Example 3) that the silicon-aluminum alloy phase change microcapsules are encapsulated in the ceramic fiber network. The content of the silicon-aluminum alloy phase change microcapsules in b (Example 1) is relatively low. It can be seen from d (Example 5) that the silicon-aluminum alloy phase change microcapsules are stacked and there is adhesion in the fiber network. This may be due to the excessive content of the silicon-aluminum phase change microcapsules. The excessive content of the silicon-aluminum phase change microcapsules has affected the microstructure of the ceramic fiber aerogel network. Figure 3 This is the microscopic enlarged morphology of the sample of Example 3. Under the scale of 300 μm, a large number of silicon-aluminum alloy phase change microcapsules can be seen, which are relatively evenly distributed in the ceramic fiber network. And the silicon-aluminum alloy phase change microcapsules and the ceramic fibers are in-situ encapsulated by electrospinning. Therefore, during the curing-sintering and heat insulation performance tests, no falling-off phenomenon occurs, indicating that the ceramic fiber aerogel has good heat insulation effect.

[0085] X-ray diffraction was used to explore the influence of the sintering temperature on the structure of the ceramic fiber aerogel. Figure 4 This is the XRD pattern of the ceramic fiber aerogels prepared in Examples 3-4 and Comparative Examples 2-4. It can be seen from the figure that when the sintering temperatures of Comparative Examples 2 and 3 are 600 °C and 750 °C respectively, there are no particularly obvious characteristic peaks of SiC in the samples. When the sintering temperature is 800 °C (Example 4), characteristic peaks of SiC appear at 36.5° (111), 60.0° (220), and 71.8° (311). When the sintering temperature is 1000 °C (Example 3), characteristic peaks of SiC appear at 36.5° (111), 60.0° (220), and 71.8° (311). However, when the sintering temperature is 1250 °C (Comparative Example 4), the characteristic peak of SiC that appears at 61.7° (220) disappears, indicating that with the excessive sintering temperature, the Si-C bond is broken, generating free carbon or SiO 2 heterogeneous phase, reducing the fiber purity and thus affecting the heat insulation performance.

[0086] Figure 5 This is the DSC diagram of the prepared ceramic fiber aerogel and the silicon-aluminum alloy phase change microcapsules. It can be seen that the ceramic fiber aerogel has an obvious endothermic peak at 570-580 °C, indicating that the ceramic fiber aerogel undergoes a phase change transformation at 570 °C, and the silicon-aluminum alloy phase change microcapsules absorb heat during the transformation from the solid phase to the liquid phase. This in-situ phase change behavior can effectively inhibit the temperature rise rate and peak temperature of the battery, significantly improving the thermal stability of the battery. At the same time, the heat insulation effect of the ceramic fiber aerogel can also block the rapid transfer of heat, synergistically improving the overall thermal management efficiency of the entire thermal management system. Combining with the SEM diagram, it can be known that the silicon-aluminum alloy phase change microcapsules are successfully encapsulated into the SiC ceramic fibers, and during the sintering process, the phase change microcapsules do not show phenomena such as breakage and leakage.

[0087] The effect of high-temperature (>800 °C) ablation on the thermal insulation performance of ceramic fiber aerogel was studied using an infrared thermal imager, as Figure 6 shown. Among them, a and b are the physical picture and the thermal imaging diagram of the heating surface temperature distribution of the ceramic fiber aerogel prepared in Example 3 under the ablation of a butane spray gun. It can be seen that the ceramic fiber aerogel structure is intact under the ablation of an 839 °C flame and can effectively resist the direct ablation of high-temperature flames. c and d are the thermal imaging diagrams of the back surface temperature distribution of the ceramic fiber aerogel prepared in Example 3 after heating for 30 s and 120 s. It can be seen from the figure that when heating for 30 s, the back surface temperature of the ceramic fiber aerogel is only 73.3 °C. When heating for 120 s, the back surface temperature reaches 124.3 °C, indicating that the ceramic fiber aerogel prepared in Example 3 has good thermal insulation performance. e, f, and g are the thermal imaging diagrams of the back surface temperature distribution of the ceramic fiber aerogel prepared in Example 2, Example 1, and Example 5 after heating for 120 s, and the back surface temperatures are 192 °C, 210 °C, and 217 °C respectively. It can be seen that as the phase change microcapsules increase, the back surface temperature first decreases and then increases. Combining the scanning electron microscope analysis, it can be known that excessive addition of microcapsules will fill or block the gaps between fibers, reducing the overall porosity of the material, resulting in heat being more easily transferred through the solid phase rather than being isolated by pores, thereby reducing the thermal insulation performance of the ceramic fiber aerogel. h and i are the thermal imaging diagrams of the back surface temperature of the ceramic fiber aerogel of Comparative Example 6 and Comparative Example 1 after heating for 120 s. It can be seen that when no phase change microcapsules are added, the back surface temperature of the ceramic fiber aerogel is as high as 237.8 °C, and the back surface temperature of the ceramic fiber aerogel prepared by impregnation after heating for 120 s is 226.3 °C, and its thermal insulation performance is poorer than that of the ceramic fiber aerogel prepared in Example 3.

[0088] The above embodiments are only some embodiments with better effects of the present invention, but the embodiments of the present invention are not limited by the above embodiments. Any equivalent replacement, deformation, and modification of some technical features within the creative concept and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a high-temperature phase-change thermal insulation ceramic fiber aerogel, characterized in that: Here are the steps: Step 1, adding polycarbosilane and polyvinyl pyrrolidone to an organic solvent and mixing and stirring until completely dissolved to obtain a precursor solution; the mass ratio of the polycarbosilane to the polyvinyl pyrrolidone is (1-2):(1-2); the ratio of the mass of the polycarbosilane to the volume of the organic solvent is (1-2) g:(7-25) mL; Step 2, dispersing the high-temperature phase change microcapsules into the precursor solution, stirring until the dispersion is uniform, and obtaining a spinning solution; the mass ratio of the polycarbosilane to the high-temperature phase change microcapsules is (1-2): (2-10); the high-temperature phase change microcapsules are silicon-aluminum alloy phase change microcapsules, the phase change temperature of the silicon-aluminum alloy phase change microcapsules is 550-600°C, and the phase change enthalpy is 400-500 J / g; Step 3, electrospinning the spinning solution to obtain a ceramic precursor fiber membrane containing high-temperature phase change microcapsules; Step 4: cross-linking, curing and sintering the ceramic precursor fiber membrane to obtain a high-temperature phase change thermal insulation ceramic fiber aerogel.

2. The preparation method according to claim 1, characterized in that: The organic solvent is one or more of N,N-dimethylformamide, tetrahydrofuran, and isopropanol.

3. The preparation method according to claim 1, characterized in that: The mixing time in step 1 is 1 to 3 h.

4. The preparation method according to claim 1, characterized in that: The preparation method of the silicon-aluminum alloy phase-change microcapsules is as follows: immersing micron-sized silicon-aluminum alloy powder in silica sol, performing heat treatment at 100-200° C. for 2-4 hours to form a silica shell layer on the particle surface, and obtaining silica-coated silicon-aluminum alloy phase-change microcapsules, wherein the mass ratio of the micron-sized silicon-aluminum alloy powder to the silica sol is 1:8-10.

5. The preparation method according to claim 1, characterized in that: The process parameters of the electrospinning in step 3 are: spinning voltage 8-18 kV, the distance between the spinneret and the receiver roller is 10-20 cm, the roller speed is 150-300 rpm, and the injector flow rate is 1-3 mL / h.

6. The preparation method according to claim 1, characterized in that: The cross-linking curing temperature in step 4 is 150° C. to 200° C., and the time is 1 to 2 h.

7. The preparation method according to claim 1, characterized in that: The sintering system is: heating to 800°C-1200°C at a heating rate of 5°C / min in a nitrogen atmosphere and keeping the temperature for 1-3 hours.

8. A high temperature phase change thermal insulation ceramic fiber aerogel, characterized in that: The ceramic fiber aerogel is prepared by the preparation method according to any one of claims 1 to 7, wherein the ceramic fiber aerogel is a three-dimensional network structure in which high-temperature phase change microcapsules are in-situ encapsulated in a ceramic fiber network, and the thermal conductivity is 0.035 to 0.050 W·m -1 ·K -1 .

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