Gradient structure ceramic fiber composite felt and method for preparing the same

Abstract

This invention relates to the field of thermal insulation materials, specifically to a gradient-structured ceramic fiber composite felt and its preparation method. From bottom to top, the felt consists of a surface layer A1, a core layer B, and a surface layer A2, with gradient transition interfaces between each layer. The slurry A of surface layers A1 and A2 is composed of water, long ceramic fibers, glass microspheres, and a composite adhesive. The slurry B of the core layer B is composed of water, SiO2 aerogel, inorganic functional fillers, short ceramic fibers, a composite light-blocking agent, and a flocculant. This invention, through a gradient structure design, organically combines a high-strength, wear-resistant surface layer with an ultra-low thermal conductivity, highly protective core layer. By introducing inorganic functional fillers into the core layer, a unique active thermal protection system is constructed. When exposed to high temperatures, the material not only passively insulates with the low thermal conductivity of the aerogel but also actively dissipates heat and blocks heat conduction through the endothermic decomposition of the fillers and the in-situ self-generation of a secondary ceramic insulation layer.

Description

Technical Field

[0001] This invention relates to the field of thermal insulation materials technology, specifically to gradient structure ceramic fiber composite felt and its preparation method. Background Technology

[0002] With the global energy transition and increased awareness of safety, high-performance thermal insulation materials are increasingly being used in key areas such as power batteries for new energy vehicles, energy storage power stations, industrial fire protection, and energy-efficient buildings. Particularly in the field of new energy vehicles, developing thermal insulation materials that can effectively block heat transfer at extreme temperatures and buy valuable time for evacuation and emergency response has become a pressing technical challenge for the industry, addressing the severe safety challenges posed by lithium battery thermal runaway.

[0003] Aerogels, due to their unique nanoporous structure and extremely low thermal conductivity, are used in thermal insulation materials. However, pure aerogel materials are usually in powder or brittle block form, with poor mechanical properties, making them difficult to apply directly. Therefore, combining aerogels with reinforcing skeletons such as fibers to prepare aerogel composite boards / felts with certain mechanical strength is currently the mainstream technical route. In the preparation process of aerogel composite materials, the wet molding process has received widespread attention from the industry because it can achieve uniform mixing of various components, has a relatively simple process flow, and is environmentally friendly. It usually uses water as a medium and there is no evaporation of organic solvents. This process typically involves dispersing fibers, aerogel powder, binders, etc. in water to form a slurry, and then dehydrating, molding, drying, and curing to obtain the final product.

[0004] For example, patent CN114634331A discloses an aerogel-modified glass fiber insulation board and its preparation method. This technology disperses coarse and fine glass fibers with aerogel and black materials in a liquid to form a mixed slurry, then dehydrates it through vacuum or pressing to form a felt, applies an adhesive, and cures it at high temperature. This patent improves the overall performance of the product to some extent by homogenizing fibers of different sizes, using coarse fibers to build the framework and fine fibers to fill the pores. However, in-depth research and practice have revealed that existing wet molding technologies, including the aforementioned patent, still have the following inherent defects that are difficult to overcome: First, there is an inherent contradiction and ceiling effect in performance. The core idea of ​​existing technologies is "homogeneous mixing," which means uniformly distributing all functional components throughout the entire material volume. This design inevitably leads to mutual constraints on performance. To improve mechanical strength, the ratio of fiber to binder must be increased, but this introduces more thermal bridges, sacrificing thermal insulation performance; conversely, to pursue extremely low thermal conductivity, the aerogel content is increased, making the product overall loose and fragile, with low surface hardness and easy powdering, making it difficult to meet the requirements of actual assembly and long-term use. This seesaw effect creates a ceiling in the overall performance of homogeneous materials that is difficult to overcome. Secondly, the homogeneous hybrid design concept fails to consider the different functional requirements of different parts of the insulation panel. For example, the surface requires high strength, wear resistance, and impact resistance, while the core requires extremely low density and high porosity. The homogeneous structural design results in the material's performance not being optimally configured spatially, leading to a waste of material potential. Furthermore, current technologies primarily rely on the low thermal conductivity of materials to achieve passive insulation. In extreme scenarios such as battery thermal runaway, where massive heat and energy are released instantaneously, this passive method of delaying heat conduction proves inadequate. The materials themselves lack the ability to actively absorb heat energy, self-reinforce themselves at high temperatures, or undergo beneficial chemical reactions; the protection mechanism is simplistic, and safety redundancy is insufficient.

[0005] In summary, how to overcome the limitations of the traditional wet molding process's homogeneous mixing approach and develop an aerogel composite thermal insulation material with optimized structural design, active protection mechanism, and good overall performance is a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of this invention is to provide a gradient structure ceramic fiber composite felt with ultra-low thermal conductivity and active thermal protection capability.

[0007] The present invention also provides a preparation method that is simple, easy to implement, and suitable for large-scale production.

[0008] The gradient structure ceramic fiber composite felt of the present invention comprises, from bottom to top, a surface layer A1, a core layer B, and a surface layer A2. A gradient transition interface exists between surface layer A1 and core layer B, and between core layer B and surface layer A2. Within this gradient transition interface, the components constituting surface layers A1 and A2 interpenetrate and are physically bonded to the components constituting core layer B. Surface layers A1 and A2 impart excellent mechanical strength, surface hardness, and wear resistance to the composite felt. Core layer B imparts ultra-low thermal conductivity and active thermal protection capabilities to the composite felt, enabling it to undergo endothermic decomposition and in-situ self-generation of a ceramic insulation layer at high temperatures.

[0009] The slurry A of surface layer A1 and surface layer A2 is composed of the following components in parts by mass:

[0010] Water: 25,000 servings;

[0011] Long ceramic fibers: 120-180 parts;

[0012] Glass microspheres: 15-25 parts;

[0013] 130-190 parts of composite adhesive;

[0014] The slurry B of the core layer B is composed of the following components in parts by mass:

[0015] Water: 20,000 servings;

[0016] SiO2 aerogel: 200-300 parts;

[0017] Inorganic functional fillers: 75-180 parts;

[0018] Short ceramic fibers: 25-35 parts;

[0019] Composite sunblock: 25-35 parts;

[0020] Flocculant: 0.01%-0.5% of the oven-dry solids weight of slurry B;

[0021] The long ceramic fiber has a diameter ≤10μm and a length of 0.8-1cm;

[0022] The short ceramic fiber has a diameter of ≤10μm and a length of 1-3mm.

[0023] The composite adhesive is a mixture of silica sol, acrylic adhesive, and PVA solution in a mass ratio of (70-100):(10-20):(50-70). PVA and acrylic adhesive primarily provide flexible bonding and green strength in the low-temperature region, while the silica sol forms a rigid inorganic network at high temperatures, providing ultimate high-temperature structural stability.

[0024] The inorganic functional filler is a mixture of inorganic hydroxide flame retardant and low melting point glass powder.

[0025] Preferably, the inorganic functional filler is a mixture of inorganic hydroxide flame retardant and low melting point glass powder in a mass ratio of (60-150):(15-30).

[0026] More preferably, the inorganic hydroxide flame retardant is aluminum hydroxide (ATH) and / or magnesium hydroxide (MDH).

[0027] The melting point of the low-melting-point glass powder is higher than the initial decomposition temperature of the inorganic hydroxide flame retardant, but lower than 700°C.

[0028] The composite light-blocking agent is a mixture of a reflective infrared light-blocking agent and an absorptive light-blocking agent in a mass ratio of (10-20):(5-25).

[0029] The reflective infrared opacifier is titanium dioxide, and the absorptive opacifier is one or both of carbon black and silicon carbide.

[0030] The method for preparing the gradient structure ceramic fiber composite felt of the present invention comprises the following steps:

[0031] I. Slurry Preparation:

[0032] A. Slurry preparation:

[0033] Add long ceramic fibers, glass microspheres, and composite adhesive to water, and stir at 800-1000 r / min for 8-12 min until uniform to obtain slurry A;

[0034] B. Slurry preparation:

[0035] Add SiO2 aerogel, inorganic functional filler, short ceramic fiber and composite opacifier to water and stir at 1400-1600 r / min for 12-18 min. Add flocculant before the end of stirring to obtain slurry B.

[0036] II. Step-by-step integrated molding:

[0037] Inject slurry A, which forms the surface layer A1, into the molding machine. Start the vacuum pump for 3-8 seconds of pre-dehydration to form a semi-solidified bottom layer. Then stop the pump. Next, inject all of slurry B evenly at multiple points at a height of 10-20cm on the surface of the injected slurry A. Finally, inject the remaining slurry A evenly at multiple points at a height of 10-20cm on the surface of the injected slurry B, so that it evenly covers the slurry B, forming an A1-B-A2 layered wet preform.

[0038] III. Dehydration and Thickness Fixing:

[0039] Start the vacuum pump for primary dehydration. After there is no obvious flowing water on the surface, cover with filter cloth and use a press at a pressure of 0.05-0.2MPa for auxiliary dehydration. Finally, press the wet blank to 110%-120% of the target thickness to obtain the intermediate.

[0040] IV. Drying and Curing:

[0041] The wet preform after thickness determination is fed into a tunnel drying line. It is first pre-cured in a low-temperature zone of 100-120℃ for 25-40 minutes. Then it is pre-cured in a high-temperature zone of 210-230℃ for 35-50 minutes to complete the final curing and drying.

[0042] The final product is a gradient-structured ceramic fiber composite felt with a thickness of 1-5 mm and a density of 300-350 kg / m³. 3 .

[0043] This invention designs an organic-inorganic two-stage curing and bonding system, employing a two-step temperature zone drying curve during the drying and curing process. In the low-temperature zone (100-120℃), moisture evaporates, and PVA and acrylic adhesive first form a flexible organic bonding network, giving the wet blank and semi-finished product sufficient "green strength" to prevent cracking. In the high-temperature zone (200-230℃), the silica sol dehydrates and condenses, forming a rigid Si-O-Si three-dimensional network framework, providing high-temperature stability and structural strength to the final product. Simultaneously, some organic matter may slightly carbonize, further filling the pores.

[0044] This synergistic combination of process and formulation results in a hybrid network of inorganic rigid skeleton and organic flexible filler in the final product, which combines structural stability at high temperatures with vibration resistance and impact toughness at room temperature.

[0045] Meanwhile, this invention employs a wide-temperature-range infrared light-blocking agent synergistic system, namely, the combined use of reflective and absorptive light-blocking agents.

[0046] In slurry B, we not only add carbon black or silicon carbide (SiC) absorbing materials, but also titanium dioxide (TiO2), a reflective material. In the mid-temperature range (<600℃), TiO2 has a strong ability to scatter and reflect infrared radiation. In the high-temperature range (>600℃), SiC and carbon black mainly prevent heat transfer by absorbing infrared radiation. By combining these two mechanisms of light-blocking agents, the heat insulation core layer has an extremely high ability to suppress thermal radiation throughout the entire operating range from low to high temperatures, far exceeding the performance of a single light-blocking agent.

[0047] The ceramic fiber felt produced by this invention possesses a "self-generated gradient" interface layer, forming a physically interpenetrating gradient interface through process control. After adding slurry A and subjecting it to brief, slight dehydration, slurry B is immediately injected while the slurry is still in a semi-fluid, semi-solidified state, without waiting for it to completely settle or solidify. Utilizing the finer fibers, aerogel powder, and other particles in slurry B, along with the impact force of the fluid, it naturally penetrates a short distance into the surface pores of the coarse fiber network of slurry A. This results in a gradient transition layer where components A and B interpenetrate and interlock, rather than a clear A / B interface. This transition layer significantly enhances the physical interlocking force between layers, and its resistance to interlayer peeling is far higher than that of simple physical bonding, fundamentally eliminating the risk of delamination.

[0048] This invention incorporates inorganic functional fillers in core layer B. When thermal runaway occurs and heat penetrates surface layer A to reach core layer B, ATH and MDH absorb a massive amount of heat energy through their own chemical decomposition reactions, thus significantly inhibiting the rapid temperature rise of the core layer. The effect is similar to the heat absorption platform of phase change materials, but with a wider operating temperature range and a more substantial total heat absorption. The decomposition reaction releases a large amount of non-toxic, non-flammable water vapor. This water vapor can dilute flammable gases such as electrolyte volatiles, acting as a suffocating flame retardant; furthermore, the evaporation and diffusion of the water vapor itself carries away a significant amount of heat, cooling the environment. The solid products remaining after the decomposition reaction are alumina (Al2O3) and magnesium oxide (MgO), both of which are ultra-high temperature resistant ceramic materials. At this point, the added low-melting-point glass powder softens and melts at high temperatures, binding the Al2O3 and MgO powders together. Furthermore, as the water vapor escapes, it leaves numerous pores in this newly formed ceramic layer. Ultimately, a completely new, dense, porous ceramic thermal insulation barrier that can withstand higher temperatures is formed in situ inside the core layer. This "secondary insulation layer" can effectively prevent heat from penetrating further, achieving an intelligent upgrade from passive insulation to actively generating a stronger insulation layer upon contact with fire.

[0049] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0050] (1) This invention breaks through the technical bottleneck of traditional homogeneous mixing. Through the A1-B-A2 gradient structure design, a high-strength, wear-resistant surface layer is organically combined with an ultra-low thermal conductivity, strong protective core layer. This structure optimizes the performance of different parts of the material, solves the inherent contradiction between thermal insulation and mechanical strength, and achieves comprehensive performance far exceeding that of homogeneous materials.

[0051] (2) This invention introduces inorganic functional fillers into the core layer B to construct a unique "active thermal protection" system. When exposed to high temperatures, the material can not only passively insulate against heat by relying on the low thermal conductivity of the aerogel, but also actively consume heat energy and block heat conduction through the heat absorption decomposition of the filler and the in-situ self-generation of a secondary ceramic insulation layer.

[0052] (3) The present invention adopts a unique step-by-step integral molding process. By briefly pre-dehydrating the bottom layer A1 slurry and controlling the timing and method of subsequent slurry injection, a self-generated gradient interface with mutual penetration and physical locking of components is formed between the layers. This interface greatly enhances the interlayer bonding force and fundamentally solves the technical problem of easy delamination of multilayer composite materials.

[0053] (4) The preparation method of the present invention can be achieved simply by adjusting the feeding sequence and dehydration rhythm on the basis of traditional wet molding equipment, without the need for additional complex equipment investment. The entire molding process is continuous and efficient, realizing the integrated preparation of complex gradient structures, and has strong industrial production feasibility and cost advantages. Detailed Implementation

[0054] The present invention will be further described below with reference to the embodiments.

[0055] Unless otherwise specified, all raw materials used in the examples were commercially available.

[0056] Long ceramic fibers (alumina silicate fibers): filament diameter ≤10μm, length 0.8-1cm, purchased from Hebei Qingjiang New Material Technology Co., Ltd.

[0057] Short ceramic fibers (alumina silicate fibers): filament diameter ≤10μm, length 1-3mm, purchased from Hebei Qingjiang New Material Technology Co., Ltd.;

[0058] Glass microspheres: 60 mesh, purchased from Lingshou County Chenyang Mineral Products Co., Ltd.;

[0059] Silica sol: concentration 30 wt.%, purchased from Hubei Xingdongcheng Chemical Co., Ltd.

[0060] Acrylic adhesive: SAC-100, diluted with water to 44 wt.%, purchased from Shanghai Youen Chemical Co., Ltd.;

[0061] PVA solution: 5 wt.% solution of PVA 17-88;

[0062] SiO2 aerogel: thermal conductivity 0.003 W / (m·K), 600 mesh, purchased from Guangdong Zhongyouli Technology Co., Ltd.;

[0063] Aluminum hydroxide (ATH), particle size 1-3 μm;

[0064] Magnesium hydroxide: MDH, particle size 1-3μm;

[0065] Low melting point glass powder: melting point 450℃, particle size 1-3μm, purchased from Shijiazhuang Shiye Mineral Products Co., Ltd.

[0066] Titanium dioxide: 100 mesh particle size;

[0067] Silicon carbide: 100 mesh particle size;

[0068] Flocculant: Cationic polyacrylamide (CPAM).

[0069] Example 1

[0070] The method for preparing the gradient structure ceramic fiber composite felt comprises the following steps:

[0071] I. Slurry Preparation:

[0072] Preparation of slurry A: Add 150g of long ceramic fibers, 20g of glass microspheres, 80g of silica sol, 15g of acrylic adhesive, and 60g of PVA solution to 25kg of water, and stir at 800r / min for 10min to obtain slurry A.

[0073] Preparation of slurry B: Add 250g of SiO2 aerogel powder, 80g of aluminum hydroxide, 20g of low melting point glass powder, 30g of short ceramic fiber, 15g of titanium dioxide, and 10g of silicon carbide to 20kg of water, stir at 1500r / min for 15min, and finally add 0.405g of flocculant and mix well to obtain slurry B.

[0074] II. Step-by-step integrated molding:

[0075] Place buffer water at the bottom of the molding machine, quickly inject half of the A slurry, and start the vacuum pump to dehydrate for 5 seconds to form a semi-solidified bottom layer. Then stop the pump and evenly inject all of the B slurry at multiple points at a height of 10cm above the surface of the already injected A slurry. Finally, evenly inject the remaining A slurry at multiple points at a height of 10cm above the surface of the already injected B slurry, so that it evenly covers the B slurry, forming an A1-B-A2 layered wet preform.

[0076] III. Dehydration and Thickness Fixing:

[0077] Start the vacuum pump for primary dewatering. After there is no obvious flowing water on the surface, cover with filter cloth and use a press to pressurize to 0.1MPa for auxiliary dewatering, and finally press the wet blank to a thickness of 3.5mm;

[0078] IV. Drying and Curing:

[0079] The wet blank, after thickness determination, is fed into a tunnel-type drying line. First, it runs in a low-temperature zone of 110±10℃ for 30 minutes to allow the PVA and acrylic adhesive to initially crosslink. Then, it runs in a high-temperature zone of 220±10℃ for 40 minutes to completely solidify the silica sol and evaporate all residual moisture, resulting in a finished product with a final thickness of 3mm.

[0080] Example 2

[0081] The method for preparing the gradient structure ceramic fiber composite felt comprises the following steps:

[0082] I. Slurry Preparation:

[0083] Preparation of slurry A: Add 120g of long ceramic fibers, 15g of glass microspheres, 70g of silica sol, 12g of acrylic adhesive, and 50g of PVA solution to 25kg of water, and stir at 800r / min for 10min to obtain slurry A.

[0084] Preparation of slurry B: Add 200g of SiO2 aerogel powder, 100g of aluminum hydroxide, 50g of magnesium hydroxide, 30g of low melting point glass powder, 25g of short ceramic fibers, 10g of titanium dioxide, 20g of silicon carbide, and 5g of carbon black to 20kg of water. Stir at 1500r / min for 15min. Finally, add 0.044g of flocculant and mix well to obtain slurry B.

[0085] II. Step-by-step integrated molding:

[0086] Place buffer water at the bottom of the molding machine, quickly inject half of the A slurry, and start the vacuum pump to dehydrate for 5 seconds to form a semi-solidified bottom layer. Then stop the pump and evenly inject all of the B slurry at multiple points at a height of 10cm above the surface of the already injected A slurry. Finally, evenly inject the remaining A slurry at multiple points at a height of 10cm above the surface of the already injected B slurry, so that it evenly covers the B slurry, forming an A1-B-A2 layered wet preform.

[0087] III. Dehydration and Thickness Fixing:

[0088] Start the vacuum pump for primary dewatering. After there is no obvious flowing water on the surface, cover with filter cloth and use a press to pressurize to 0.1MPa for auxiliary dewatering, and finally press the wet blank to a thickness of 3.5mm;

[0089] IV. Drying and Curing:

[0090] The wet blank, after thickness determination, is fed into a tunnel-type drying line. First, it runs in a low-temperature zone of 110±10℃ for 30 minutes to allow the PVA and acrylic adhesive to initially crosslink. Then, it runs in a high-temperature zone of 220±10℃ for 40 minutes to completely solidify the silica sol and evaporate all residual moisture, resulting in a finished product with a final thickness of 3mm.

[0091] Example 3

[0092] The method for preparing the gradient structure ceramic fiber composite felt comprises the following steps:

[0093] I. Slurry Preparation:

[0094] Preparation of Slurry A: Add 180g of long ceramic fibers, 25g of glass microspheres, 100g of silica sol, 18g of acrylic adhesive, and 70g of PVA solution to 25kg of water, and stir at 800r / min for 10min to obtain slurry A.

[0095] Preparation of slurry B: Add 300g of SiO2 aerogel powder, 60g of aluminum hydroxide, 15g of low melting point glass powder, 35g of short ceramic fibers, 20g of titanium dioxide, and 5g of silicon carbide to 20kg of water. Stir at 1500r / min for 15min. Finally, add 2.175g of flocculant and mix well to obtain slurry B.

[0096] II. Step-by-step integrated molding:

[0097] Place buffer water at the bottom of the molding machine, quickly inject half of the A slurry, and start the vacuum pump to dehydrate for 5 seconds to form a semi-solidified bottom layer. Then stop the pump and evenly inject all of the B slurry at multiple points at a height of 10cm above the surface of the already injected A slurry. Finally, evenly inject the remaining A slurry at multiple points at a height of 10cm above the surface of the already injected B slurry, so that it evenly covers the B slurry, forming an A1-B-A2 layered wet preform.

[0098] III. Dehydration and Thickness Fixing:

[0099] Start the vacuum pump for primary dewatering. After there is no obvious flowing water on the surface, cover with filter cloth and use a press to pressurize to 0.1MPa for auxiliary dewatering, and finally press the wet blank to a thickness of 3.5mm;

[0100] IV. Drying and Curing:

[0101] The wet blank, after thickness determination, is fed into a tunnel-type drying line. First, it runs in a low-temperature zone of 110±10℃ for 30 minutes to allow the PVA and acrylic adhesive to initially crosslink. Then, it runs in a high-temperature zone of 220±10℃ for 40 minutes to completely solidify the silica sol and evaporate all residual moisture, resulting in a finished product with a final thickness of 3mm.

[0102] Non-preferred embodiment 4

[0103] Same as Example 1, except that:

[0104] B. Slurry preparation: Add 250g of SiO2 aerogel powder, 100g of aluminum hydroxide (replacing the original 80g aluminum hydroxide + 20g glass powder), 30g of short ceramic fibers, 15g of titanium dioxide, and 10g of silicon carbide to 20kg of water, stir at 1500r / min for 15min, and finally add flocculant and mix well.

[0105] Comparative Example 1

[0106] Using the same total material quantity as in Example 1, all materials were mixed at once in 45 kg of water and stirred at 1500 r / min for 15 min to form a homogeneous slurry. The slurry was then injected into a molding machine for one-time dehydration, thickness determination, and drying at a constant temperature of 220±10℃ for 90 min.

[0107] Comparative Example 2

[0108] The raw materials and processes are exactly the same as in Example 1, but the B slurry does not contain ATH and low melting point glass powder. To compensate for the solid content, the SiO2 aerogel powder is increased to 350g.

[0109] Comparative Example 3

[0110] Same as Example 1, except that:

[0111] II. Step-by-step integrated molding

[0112] Place buffer water at the bottom of the molding machine, quickly inject half of the A slurry, start the vacuum pump to dehydrate until solidified, and evenly inject all of the B slurry at multiple points at a height of 10cm above the surface of the already injected A slurry. Start the vacuum pump to dehydrate until solidified. Finally, evenly inject the remaining A slurry at multiple points at a height of 10cm above the surface of the already injected B slurry, so that it evenly covers the B slurry. Start the vacuum pump to dehydrate until solidified, forming an A1-B-A2 layered wet preform.

[0113] The samples prepared in the examples and comparative examples were compared with those prepared in Comparative Example 1 using a conventional homogenization mixing process. The surface hardness was tested using a Shore C hardness tester according to GB / T 2411-2008, the interlayer peel strength was tested using GB / T 2790-1995, and the thermal conductivity was tested using GB / T 10294-2008.

[0114] 700℃ thermal shock test: The single-sided thermal shock test, which simulates battery thermal runaway, is used to evaluate the performance of thermal insulation materials in suppressing heat transfer and protecting adjacent areas when simulating thermal runaway of a single battery cell.

[0115] Test apparatus:

[0116] This test uses a single-sided thermal shock test bench, which mainly consists of the following parts:

[0117] High-temperature heating source: A quartz lamp array heater is used, which can provide a stable hot surface temperature of ≥800℃ and has the ability to heat up rapidly. The heating area is larger than the sample area.

[0118] Sample clamping system: It is made of high-temperature resistant ceramic fiber frame, which is used to fix the sample to be tested, and at the same time insulate the sample edge to reduce the edge heat dissipation effect.

[0119] Temperature monitoring system:

[0120] Hot surface temperature monitoring: A type K armored thermocouple is used, which is placed in close contact with the center point of the heating source surface to control and record the hot surface temperature.

[0121] Cold side (back temperature) monitoring: A K-type patch thermocouple is used and fixed to the center point of the cold side of the sample under test with high-temperature tape to record key back temperature change data.

[0122] Test steps:

[0123] Sample preparation: Cut the insulation material to be tested into standard samples of 80mm×80mm.

[0124] Equipment preheating: Turn on the heating source to preheat and stabilize it at the target temperature of 700±10℃.

[0125] Sample installation: Quickly install the sample equipped with the cold-face thermocouple into the sample clamping system, with its heated surface facing the heating source.

[0126] Start the test: As soon as the sample is installed in place, start the data acquisition system to record time-temperature data. The total test duration is 300 seconds.

[0127] Extract the following key performance indicators from the recorded data:

[0128] Time required for back surface temperature to reach 200°C: Record the time from the start of the test (t=0) to the first time the cold surface temperature reaches 200°C.

[0129] Back surface temperature after 300 seconds: Record the final value of the cold surface temperature after 300 seconds of testing.

[0130] The design of this test method mainly refers to and simulates the test requirements for "cell thermal runaway" in GB 38031-2020 "Safety Requirements for Power Batteries for Electric Vehicles". This national standard requires that the battery pack should not catch fire or explode within 5 minutes after a single cell thermal runaway occurs, providing an escape warning for occupants. The selection of a heating temperature of 700℃ is to simulate a representative and severe operating condition of the typical peak temperature range that the surface of the lithium battery casing may reach during thermal runaway. The selection of a 5-minute (300-second) test duration directly corresponds to the "5-minute" safety warning window period specified in GB 38031-2020.

[0131] The 200℃ back temperature threshold is an industry-recognized critical safety temperature used to assess whether adjacent cells will be thermally induced to trigger their own thermal runaway. The thermal runaway trigger temperature of most lithium batteries is between 130℃ and 200℃, therefore 200℃ is considered a key failure point.

[0132] The test results are shown in Table 1 below:

[0133] Table 1 Test Results

[0134] The room temperature performance of Non-Preferred Example 4 was almost identical to that of Example 1, demonstrating the effectiveness of experimental variable control. However, its performance deteriorated significantly in the 700°C thermal shock test. The time for the back temperature to reach 200°C decreased from 213 seconds to 182 seconds, and the back temperature surged from 242°C to 305°C after 5 minutes. This strongly demonstrates the indispensability of low-melting-point glass powder. In Comparative Example 4, although aluminum hydroxide also undergoes endothermic decomposition at high temperatures, leaving solid alumina, without the fusion bonding effect of low-melting-point glass powder, the newly formed Al2O3 is merely a loose powder and cannot form a dense, robust secondary ceramic insulation layer. Heat can easily continue to transfer to the cold surface through the gaps between the powder particles, and may even be carried away by the airflow when water vapor escapes, forming a continuous thermal channel. Therefore, although there is a brief delay in the endothermic decomposition process, a durable and effective thermal barrier cannot be formed.

[0135] Comparative Example 1 used the same material formulation as Example 1, but was formed in one step through homogeneous mixing. The surface hardness of Example 1 was significantly higher than that of Comparative Example 1. This is because the A layer of the present invention consists of a dense reinforcing skeleton composed of long fibers and glass microspheres, while in the homogeneous structure, the loose aerogel is distributed on the surface, resulting in low hardness and easy breakage. Under thermal shock at 700°C, the time required for the back temperature of Example 1 to reach 200°C was 213 seconds, which was 41% longer than the 151 seconds of Comparative Example 1. This demonstrates that the synergistic effect of the gradient structure is far superior to simple homogeneous mixing. In the homogeneous structure, the long fibers running through the entire structure form thermal bridges, and the surface protection is weak, resulting in faster heat transfer. The thermal conductivity of Example 1 is also better than that of Comparative Example 1 because the concentration of aerogel in the core layer B is higher, and the dense structure of the A layer reduces air convection, which together optimizes the thermal insulation effect.

[0136] Comparative Example 2 employs the same gradient structure process as Example 1, but its core layer B contains no hydroxide flame retardant or low-melting-point glass powder; instead, it uses more aerogel. Thanks to the higher aerogel content, Comparative Example 2 has the lowest density and thermal conductivity of all samples, demonstrating excellent room-temperature insulation potential. However, in a 700°C thermal shock test, Comparative Example 2's protection time was only 167 seconds, and its back temperature reached 341°C after 5 minutes, significantly worse than Example 1. This comparison strongly demonstrates the necessity and effectiveness of the "active thermal protection" mechanism designed in this invention. Simply relying on passive insulation with low thermal conductivity is insufficient under extreme high-temperature shocks, while the endothermic decomposition and in-situ ceramic forming technology of ATH can greatly delay temperature rise, providing crucial safety redundancy.

[0137] Comparative Example 3 employs a "wet lamination" process of "laying one layer, drying one layer." This process creates two distinct "hard interfaces" with very low physical interpenetration between A1 / B and B / A2. In Comparative Example 3, the interlayer peel strength deteriorates during the clamping stage, making it impossible to obtain a valid value. This is because the fragile interface may crack prematurely under high-temperature impact, allowing heat to penetrate directly and resulting in poor thermal shock performance.

[0138] In summary, the gradient structure design, active protection mechanism, and step-by-step integrated molding process proposed in this invention work synergistically to successfully prepare a novel composite felt that combines high strength, ultra-low thermal conductivity, excellent high-temperature protection, and structural stability. Its comprehensive performance far exceeds that of existing homogeneous mixed materials and traditional laminated materials.

Claims

1. A gradient structure ceramic fiber composite felt, characterized in that, From bottom to top, the layers are surface layer A1, core layer B, and surface layer A2. There is a gradient transition interface between surface layer A1 and core layer B, and between core layer B and surface layer A2. In this gradient transition interface, the components constituting surface layer A1 and surface layer A2 and the components constituting core layer B permeate each other and are physically locked together. The slurry A of surface layer A1 and surface layer A2 is composed of the following components in parts by mass: Water: 25,000 servings; Long ceramic fibers: 120-180 parts; Glass microspheres: 15-25 parts; 130-190 parts of composite adhesive; The slurry B of the core layer B is composed of the following components in parts by mass: Water: 20,000 servings; SiO2 aerogel: 200-300 parts; Inorganic functional fillers: 75-180 parts; Short ceramic fibers: 25-35 parts; Composite sunblock: 25-35 parts; Flocculant: 0.01%-0.5% of the oven-dry solids weight of slurry B; The long ceramic fiber has a diameter ≤10μm and a length of 0.8-1cm; The short ceramic fiber has a diameter of ≤10μm and a length of 1-3mm.

2. The gradient structure ceramic fiber composite felt according to claim 1, characterized in that, The composite adhesive is a mixture of silica sol, acrylic adhesive, and PVA solution in a mass ratio of (70-100):(10-20):(50-70).

3. The gradient structure ceramic fiber composite felt according to claim 1, characterized in that, The inorganic functional filler is a mixture of inorganic hydroxide flame retardant and low melting point glass powder.

4. The gradient structure ceramic fiber composite felt according to claim 3, characterized in that, The inorganic functional filler is a mixture of inorganic hydroxide flame retardant and low melting point glass powder in a mass ratio of (60-150):(15-30).

5. The gradient structure ceramic fiber composite felt according to claim 4, characterized in that, The inorganic hydroxide flame retardant is aluminum hydroxide and / or magnesium hydroxide.

6. The gradient structure ceramic fiber composite felt according to claim 5, characterized in that, The melting point of the low-melting-point glass powder is higher than the initial decomposition temperature of the inorganic hydroxide flame retardant, but lower than 700°C.

7. The gradient structure ceramic fiber composite felt according to claim 1, characterized in that, The composite light-blocking agent is a mixture of a reflective infrared light-blocking agent and an absorptive light-blocking agent in a mass ratio of (10-20):(5-25).

8. The gradient structure ceramic fiber composite felt according to claim 7, characterized in that, The reflective infrared opacifier is titanium dioxide, and the absorptive opacifier is one or both of carbon black and silicon carbide.

9. A method for preparing a gradient structure ceramic fiber composite felt according to any one of claims 1-8, characterized in that, It is prepared by the following steps: I. Slurry Preparation: A. Slurry preparation: Add long ceramic fibers, glass microspheres, and composite adhesive to water and stir until homogeneous to obtain slurry A; B. Slurry preparation: Add SiO2 aerogel, inorganic functional filler, short ceramic fiber and composite opacifier to water and stir evenly. Add flocculant before the stirring is finished to obtain slurry B. II. Step-by-step integrated molding: Inject A slurry to form surface layer A1 into the molding machine, start the vacuum pump to pre-dehydrate it to form a semi-solidified bottom layer, then stop the pump, then evenly inject all B slurry to form core layer B, and finally evenly inject A slurry to form surface layer A2 to form a wet blank with A1-B-A2 layers.

3. The wet blank is dehydrated and its thickness is fixed to obtain the intermediate product; Fourth, the intermediate product is dried and cured in multiple temperature zones to obtain a gradient structure ceramic fiber composite felt.

10. The method for preparing the gradient structure ceramic fiber composite felt according to claim 9, characterized in that, The multi-temperature zone drying and curing specifically involves pre-curing in a low-temperature zone of 100-120℃ and final curing in a high-temperature zone of 210-230℃.

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