Sandwich-structure composite phase change material for multifunctional thermal management and preparation method of sandwich-structure composite phase change material

Abstract

The invention discloses a sandwich structure composite phase change material for multifunctional thermal management and a preparation method thereof, and belongs to the technical field of thermal management materials and phase change materials. The composite phase-change material provided by the invention has a sandwich structure, and the first layer adopts the silicon dioxide aerogel as a base material and is composed of the quartz fibers and the phase-change microcapsules, so that the composite phase-change material has high energy density and low thermal conductivity. The second layer is only made of silicon dioxide aerogel, heat interaction of the first layer and the third layer can be blocked, a relatively independent thermal environment is maintained, and meanwhile possible thermal breakdown is prevented after complete phase change of the phase change microcapsules. The third layer is composed of crystalline flake graphite, phase change microcapsules and carbon fibers which are connected with one another, and the crystalline flake graphite can serve as a heat conduction framework, so that the heat conductivity in the composite phase change material is improved, the heat storage and release rate of the phase change microcapsules MPCM is increased, and temperature rise caused by heat accumulation on the surface of the material is prevented.

Description

Technical Field

[0001] This invention belongs to the technical field of thermal management materials and phase change materials, and particularly relates to a sandwich structure composite phase change material for multifunctional thermal management and its preparation method. Background Technology

[0002] With rapid industrial development and the escalating global energy crisis, the demand for effective thermal management has increased significantly, particularly in areas such as building insulation, electronic cooling, and temperature control for precision instruments. Traditional active thermal control methods relying on circulating working fluids and mechanical systems are relatively effective, but they consume significant amounts of electricity and fossil fuels during operation, increasing costs and exacerbating the greenhouse effect. Passive thermal management methods offer energy-saving and environmental advantages, but their performance largely depends on the inherent properties of the materials themselves and the structural design. Furthermore, the application of passive thermal management materials is very limited because they are often no longer suitable when thermal environments or operational requirements change. Therefore, there is an urgent need to develop advanced thermal management solutions that can address complex thermal environments, promote energy conservation, and improve the overall energy efficiency of thermal management technologies.

[0003] Phase change materials (PCMs) possess advantages such as high energy density, stable phase change temperature, and low cost and availability, demonstrating great promise in energy storage and thermal management applications. However, with the increasing complexity of thermal environments and the variability of operating conditions, PCMs with limited performance characteristics are showing signs of decline in many novel thermal management scenarios. Taking the thermal management of new batteries as an example, it is necessary not only to reduce dynamic temperature fluctuations during normal charge-discharge cycles through efficient heat dissipation, but also to prevent safety risks caused by potential battery thermal runaway. Due to the high energy density and large number of batteries, relying solely on heat absorption and storage is insufficient to completely prevent the spread of thermal runaway; insulation measures are required for protection. Therefore, the dual requirements of battery heat dissipation and thermal runaway protection place contradictory demands on the thermal conductivity of materials, which are difficult to resolve through material selection and common performance adjustments. Furthermore, when PCMs are applied to building thermal management and multi-source thermal control, the different thermal environments on both sides may also impose different performance requirements on them.

[0004] Therefore, phase change materials with single-function properties are insufficient to cope with complex thermal environments involving multifunctional requirements or multidirectional non-uniform heat sources. Thus, it is necessary to develop novel phase change thermal management materials and technologies, and design new phase change materials with differentiated properties. Summary of the Invention

[0005] To address the limitations of traditional phase change materials (PCMs) in multifunctional scenarios and complex multi-source environments, this invention proposes a sandwich-structured composite PCM for multifunctional thermal management and its preparation method. This invention proposes a layered structural strategy, employing different matrix materials combined with PCM microcapsules to achieve bidirectional regulation of thermal conductivity. Based on composite PCMs with differentiated performance, a sandwich-structured PCM with a thermal conductivity gradient is constructed, providing a novel solution for multifunctional thermal management in complex environments.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention provides a sandwich-structured composite phase change material for multifunctional thermal management. The sandwich-structured composite phase change material consists of three layers: the first layer is composed of silica aerogel (SA), quartz fiber (CQF), and phase change microcapsules (MPCM); the second layer is composed of silica aerogel (SA); and the third layer is composed of flake graphite (FG), carbon fiber (PCF), and phase change microcapsules (MPCM).

[0008] Technical Principle: This invention prepares a sandwich-structured composite phase change material using phase change microcapsules (MPCM), silica aerogel (SA), quartz fiber (CQF), flake graphite (FG), and carbon fiber (PCF) as raw materials. By combining composite phase change materials with different properties to form a sandwich structure, a composite phase change thermal management material with gradient thermal conductivity is obtained. The first layer uses silica aerogel as the matrix material, combined with quartz fiber and phase change microcapsules, exhibiting high energy density and low thermal conductivity. Due to the dense nanoporous structure of silica aerogel, it can effectively suppress air convection, and its pore walls act as a thermal barrier to reduce the material's thermal conduction and radiation. Furthermore, when nanoscale silica aerogel particles are adsorbed onto the surface of micron-sized phase change microcapsules (MPCM), a thermal barrier is formed, hindering heat transfer between the phase change microcapsules. Simultaneously, the high latent heat of the phase change microcapsules combined with the low thermal conductivity of the aerogel can significantly reduce the thermal diffusivity of the first layer, effectively delaying heat transfer within the material during transient thermal shocks (e.g., in battery thermal runaway scenarios). The second layer uses only silica aerogel, which can block the heat exchange between the first and third layers, maintaining a relatively independent thermal environment, and preventing possible thermal breakdown after the phase change microcapsules have fully undergone phase change. The third layer consists of interconnected flake graphite, phase change microcapsules, and carbon fibers. The flake graphite acts as a thermally conductive framework, improving the internal thermal conductivity of the composite phase change material, thereby accelerating the heat storage and release rate of the phase change microcapsules (MPCM) and preventing heat accumulation on the material surface that could lead to a temperature rise.

[0009] Furthermore, the thickness ratio of the first layer, the second layer, and the third layer is 1:3:1.

[0010] Furthermore, the mass percentages of the silica aerogel, quartz fiber, and phase change microcapsules in the first layer are 9.5–47.5%, 0.5–2.5%, and 50–90%, respectively.

[0011] Furthermore, the mass percentages of the flake graphite, carbon fiber, and phase change microcapsules in the second layer are 5-45%, 5%, and 50-90%, respectively.

[0012] Furthermore, the phase change microcapsules have an average particle size of 2–5 μm; the phase change microcapsules have a core-shell structure; the core material of the phase change microcapsules is n-octadecane, and the shell material is melamine resin.

[0013] Furthermore, the quartz fiber has a diameter of 11 μm and a length of 3 mm.

[0014] Furthermore, the carbon fiber is selected from pitch-based carbon fiber, which has a diameter of 11 μm and a length of 2 mm.

[0015] Furthermore, the flake graphite has sheet diameters of 10 μm, 50 μm, and 100 μm, and a thickness of 2 μm.

[0016] This invention also provides a method for preparing the sandwich-structured composite phase change material for multifunctional thermal management as described in the above technical solution, comprising the following steps:

[0017] (1) Weigh each raw material according to the proportion;

[0018] (2) Mix silica aerogel and quartz fiber to form a matrix material; add phase change microcapsules to the matrix material and disperse them by stirring to obtain a mixture; press and solidify the obtained mixture to form the first layer;

[0019] (3) Add silica aerogel to the first layer and hot press to form the second layer;

[0020] (4) Add a mixture of flake graphite, carbon fiber and phase change microcapsules to the second layer and continue hot pressing; after hot pressing, wait for the temperature to drop to room temperature and continue to maintain the pressure for a period of time to obtain the sandwich structure composite phase change material for multifunctional thermal management.

[0021] Further, in step (2), the pressing temperature is 60°C and the pressure is 20 MPa; and / or, the curing temperature is 60°C and the time is 6 hours; and / or,

[0022] In step (3), the hot pressing temperature is 60℃, the pressure is 20MPa, and the time is 2h; and / or,

[0023] In step (4), the hot pressing time is 6 hours; and / or the pressure is maintained for 4 hours.

[0024] Compared with the prior art, the present invention has the following advantages and technical effects:

[0025] The sandwich-structured composite phase change material with differentiated thermal conductivity provided by this invention can simultaneously solve the problems of transient thermal shock protection and surface heat dissipation and temperature control of devices and equipment. It has promising applications in many fields, including battery heat dissipation and insulation, building insulation, and precision instrument thermal control, addressing complex thermal environments in multiple directions. Unlike previous reports on phase change materials that primarily optimized thermal conductivity or insulation performance, the sandwich-structured composite phase change material proposed in this invention utilizes the complementary properties of FG / PCM and SA / PCM to achieve multifunctional thermal management. This integrated strategy enables the material to achieve effective thermal regulation in numerous application scenarios, from insulation to rapid heat dissipation, thus expanding its practical application range. Furthermore, the simplified preparation method and lower production cost of this sandwich-structured composite phase change material further enhance its competitiveness in energy-efficient thermal management solutions.

[0026] This invention innovatively introduces composite phase change materials for energy storage and thermal management from the perspective of thermal conductivity. Through differentiated design, it achieves bidirectional adjustment of the thermal conductivity of sandwich-structured composite phase change materials, solving the problems of protection against transient thermal shock and surface heat dissipation and temperature control of devices and equipment. Attached Figure Description

[0027] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0028] Figure 1 A process flow diagram of the preparation method of the sandwich-structured composite phase change material for multifunctional thermal management provided by the present invention;

[0029] Figure 2 SEM images of the composite phase change materials in Examples 3 and 8 are shown, where a is MPCM, b is SA / PCM-70, and c is FG / PCM-70; the insets are physical images.

[0030] Figure 3 The DSC diagrams of composite phase change materials with different MPCM contents are shown, where a represents SA / PCM and b represents FG / PCM.

[0031] Figure 4 The thermal conductivity diagrams are for composite phase change materials with different MPCM contents, where a represents SA / PCM and b represents FG / PCM.

[0032] Figure 5 The graphs show the thermal stability and mechanical properties of SA / PCM and FG / PCM composite phase change materials, where a represents the thermal stability of TG and b represents the compressive stress-strain curve.

[0033] Figure 6 This is a schematic diagram illustrating the effect of the sandwich-structured composite phase change material of the present invention on building indoor temperature control and battery thermal management, where a represents building indoor temperature control and b represents battery thermal management.

[0034] Figure 7 This is a comparative experiment on the thermal management performance of the nano-silica aerogel insulation board in Comparative Example 1 and the sandwich structure composite phase change material in Example 11, where a is the surface temperature response curve under transient thermal shock, and b is the boundary heat flow and surface temperature distribution under multi-directional cyclic thermal disturbance.

[0035] Figure 8 Infrared images of the nano-silica aerogel insulation board in Comparative Example 1 and the sandwich-structured composite phase change material in Example 11 under transient thermal shock test.

[0036] Figure 9 A schematic diagram of experimental equipment used for testing building thermal management performance;

[0037] Figure 10 The temperatures of the nano-silica aerogel insulation board in Comparative Example 1, the sandwich-structured composite phase change material in Example 11, and the outdoor environment are used in the building indoor thermal management experiment. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0040] This invention provides a sandwich-structured composite phase change material for multifunctional thermal management. The sandwich-structured composite phase change material consists of three layers: the first layer is composed of silica aerogel, quartz fiber and phase change microcapsules; the second layer is composed of silica aerogel; and the third layer is composed of flake graphite, carbon fiber and phase change microcapsules.

[0041] In a preferred embodiment, the thickness ratio of the first layer, the second layer, and the third layer is 1:3:1. The first layer in the composite phase change material of the present invention has high energy density and low thermal conductivity, which can effectively delay the transfer of heat in the material. The second layer can block the heat interaction between the first layer and the third layer, maintain a relatively independent thermal environment, and prevent thermal breakdown. The third layer can prevent heat accumulation on the material surface from causing the temperature to rise.

[0042] The content of phase change microcapsules and matrix materials in the first and third layers of this invention plays a key role in the balanced regulation of the thermal properties of the composite material. At the same time, by controlling the content of phase change microcapsules and matrix materials, the prepared composite phase change material has excellent morphological stability and mechanical strength.

[0043] In a preferred embodiment, the mass percentages of silica aerogel, quartz fiber, and phase change microcapsules in the first layer are 9.5–47.5%, 0.5–2.5%, and 50–90%, respectively, more preferably 19–28.5%, 1–1.5%, and 70–80%. By controlling the mass percentages of silica aerogel, quartz fiber, and phase change microcapsules within the above ranges, this invention facilitates the obtaining of a first-layer structure with low thermal conductivity and high latent heat of phase change.

[0044] In a preferred embodiment, the silica aerogel is a nano-silica aerogel; the particle size of the nano-silica aerogel is 500 nm. The nanoporous structure of the silica aerogel can effectively suppress air convection, while its pore walls act as a thermal barrier to reduce the material's heat conduction and radiation. Furthermore, when nano-sized silica aerogel particles are adsorbed onto the surface of micron-sized phase change microcapsules, a thermal barrier is formed, hindering heat transfer between the phase change microcapsules.

[0045] In a preferred embodiment, the phase change microcapsules have an average particle size of 2–5 μm; the phase change microcapsules have a core-shell structure; the core material of the phase change microcapsules is n-octadecane, and the shell material is melamine resin. The phase change microcapsules selected in this invention have a suitable phase change temperature (23–28°C) and high latent heat and fusion heat, as well as excellent shape stability, thus solving the leakage problem that may occur during the phase change process.

[0046] In a preferred embodiment, the quartz fiber has a diameter of 11 μm and a length of 3 mm.

[0047] In a preferred embodiment, the mass percentages of flake graphite, carbon fiber, and phase change microcapsules in the second layer are 5-45%, 5%, and 50-90%, respectively, more preferably 25-45%, 5%, and 50-70%. The thermal conductivity of the third layer structure in this invention significantly increases with the amount of flake graphite (FG) added, reaching 0.48-2.934 W·m. -1 ·K-1 It can be up to 13.5 times that of pure phase change microcapsules.

[0048] In a preferred embodiment, the flake graphite has sheet diameters of 10 μm, 50 μm, and 100 μm, and a thickness of 2 μm; the mass percentages of the flake graphite with diameters of 10 μm, 50 μm, and 100 μm are 17%, 17%, and 66% of the total flake graphite mass, respectively. The third layer in this invention uses flake graphite as the matrix material. The flake graphite can act as a thermally conductive framework, improving the internal thermal conductivity of the composite phase change material, thereby accelerating the heat storage and release rate of the phase change microcapsules and preventing heat accumulation on the material surface that could lead to a temperature increase.

[0049] In a preferred embodiment, the carbon fiber is selected from pitch-based carbon fiber, which has a diameter of 11 μm and a length of 2 mm.

[0050] This invention also provides a method for preparing the sandwich-structured composite phase change material for multifunctional thermal management as described in the above technical solution, comprising the following steps:

[0051] (1) Weigh each raw material according to the proportion;

[0052] (2) Mix silica aerogel and quartz fiber to form a matrix material; add phase change microcapsules to the matrix material and stir to obtain a mixture; press and solidify the obtained mixture to form the first layer;

[0053] (3) Add silica aerogel to the first layer and hot press to form the second layer;

[0054] (4) Add a mixture of flake graphite, carbon fiber and phase change microcapsules to the second layer and continue hot pressing; after hot pressing, wait for the temperature to drop to room temperature and continue to maintain the pressure for a period of time to obtain the sandwich structure composite phase change material for multifunctional thermal management.

[0055] Hot pressing, as a simple, efficient, and low-cost method for preparing composite materials, promotes interfacial bonding and densification of phase materials under controlled temperature and pressure conditions, achieving dense molding of composite materials. It effectively combines phase change materials with matrix components, constructing a stable skeletal network, thereby enabling directional control of the thermal conductivity of the composite phase change material. Therefore, this invention employs hot pressing to prepare a sandwich-structured composite phase change material, effectively forming a shape-stable and leak-free composite system while maintaining high thermal storage performance. Simultaneously, the added insulating and thermally conductive components significantly alter the thermal conductivity of the phase change composite material.

[0056] In a preferred embodiment, in step (2), the pressing temperature is 60°C and the pressure is 20MPa.

[0057] In a preferred embodiment, in step (2), the curing temperature is 60°C and the time is 6 hours.

[0058] In a preferred embodiment, in step (3), the hot pressing temperature is 60°C, the pressure is 20MPa, and the time is 2h.

[0059] In a preferred embodiment, in step (4), the continued hot pressing time is 6 hours.

[0060] In a preferred embodiment, in step (4), the pressure is maintained for 4 hours.

[0061] In this embodiment of the invention, room temperature refers to "25±2℃".

[0062] Unless otherwise specified, all raw materials used in the embodiments of this invention were purchased through commercial channels.

[0063] In the following examples and comparative examples, phase change microcapsules (MPCM) were purchased from Hefei Xineng Phase Change New Materials Technology Co., Ltd., with n-octadecane as the core phase change material and melamine resin as the outer shell encapsulation material, and an average particle size of 2–5 μm; nano-silica aerogel powder (SA) was purchased from Nanotech Co., Ltd., with a density of 0.1 g·cm³. -3 Thermal conductivity is less than 0.033 W·m -1 ·K -1 Short-cut quartz fiber (CQF) was purchased from Henan Shenjiu Tianhang New Material Co., Ltd., with a fiber diameter of 11 μm and a length of 3 mm. Flake graphite (FG) was purchased from Forsmann Technology (Beijing) Co., Ltd., with flake diameters of 10 μm, 50 μm, and 100 μm. The mass percentages of flake graphite with diameters of 10 μm, 50 μm, and 100 μm were 17%, 17%, and 66% of the total flake graphite mass, respectively. The thickness was 2 μm, and the density was 2.26 g·cm³. -3 The in-plane thermal conductivity is 523 W·m. -1 ·K -1 The thermal conductivity in the thickness direction is 38 W·m. -1 ·K -1 The pitch-based carbon fiber short strands (PCF) were purchased from Shaanxi Tianze New Material Technology Co., Ltd., with a diameter of 11 μm, a length of 2 mm, and a density of 2.15 g·cm³. -3 Thermal conductivity ≥800 W·m -1 ·K -1 Anhydrous ethanol (analytical grade) was purchased from Shanghai Titan Technology Co., Ltd.

[0064] Examples 1-5

[0065] A method for preparing a silica aerogel composite phase change material SA / PCM:

[0066] (1) Accurately weigh MPCM, SA and CQF according to their mass fractions. The mass fractions of each component in Examples 1 to 5 are shown in Table 1.

[0067] (2) Mix MPCM with 500 mL of anhydrous ethanol and stir mechanically at 900 rpm for 20 min to form a uniform suspension. Then add SA and CQF and continue stirring to ensure that each component is uniformly dispersed to obtain a mixture.

[0068] (3) Transfer the mixture obtained in step (2) to an electric heating drying oven and dry it at 80°C for 12 hours to ensure that the anhydrous ethanol is completely evaporated and obtain a powder mixture. During the drying process, gently shake the sample periodically to prevent powder agglomeration and improve the drying effect.

[0069] (4) The powder mixture obtained in step (3) was placed in a molding mold and hot-pressed at 100℃ and 20MPa for 6 hours. Then, it was cooled to room temperature at a rate of 5℃ / min and the pressure was maintained for another 4 hours. The entire hot-pressing process was carried out in a nitrogen atmosphere to avoid material oxidation. After hot pressing, the mold was removed to obtain a cylindrical silica aerogel composite phase change material SA / PCM with a diameter of 5cm, a thickness of 1cm, and a density of 0.7g·cm³. -3 .

[0070] Examples 6-10

[0071] A method for preparing a graphite composite phase change material FG / PCM:

[0072] (1) Accurately weigh MPCM, FG and PCF according to their mass fractions. The mass fractions of each component in Examples 6 to 10 are shown in Table 1.

[0073] (2) Mix MPCM with 500 mL of anhydrous ethanol and stir mechanically at 900 rpm for 20 min to form a uniform suspension. Then add FG and PCF and continue stirring to ensure that each component is uniformly dispersed to obtain a mixture.

[0074] Steps (3) to (4) are the same as in Example 1, and the density of the graphite composite phase change material FG / PCM is 0.9 g·cm³. -3 .

[0075] Table 1. Amounts of each component in the composite phase change materials of Examples 1-10

[0076]

[0077]

[0078] The microstructure of the SA / PCM and FG / PCM composite phase change materials was characterized using a Zeiss GeminiSEM 500 scanning electron microscope (SEM). Samples were fixed on the stage with conductive adhesive, sputtered with gold (Au) for 120 s, and tested at voltages ranging from 3 to 15 kV. Results are shown in [Figure number missing]. Figure 2 .

[0079] Figure 2 SEM images of the composite phase change materials in Examples 3 and 8 are shown, where a is MPCM, b is SA / PCM-70, and c is FG / PCM-70; the insets are physical images. Figure 2 As shown in section a, the phase change microcapsules exhibit a relatively intact spherical structure with a low surface damage rate, indicating that melamine resin can effectively encapsulate the phase change material and prevent its leakage. The particle size range of the phase change microcapsules is approximately 2–10 μm; compared to larger particles, the smaller particle size helps to improve the mechanical strength of the microcapsules. From… Figure 2 As can be seen from part b, in the SA / PCM composite material, a large number of aerogel particles aggregate on the surface of the phase change microcapsules, forming a structure similar to a "thermal barrier," thereby inhibiting heat conduction between microcapsules and reducing the overall effective thermal conductivity. From Figure 2 As shown in section c, the flake graphite in the FG / PCM composite material exhibits a typical lamellar structure, filling the pores between the phase change microcapsules. The flake graphite possesses high in-plane thermal conductivity, and in synergy with the high thermal conductivity carbon fibers, it constructs an efficient heat conduction network, thereby enhancing the overall heat transfer capability of the composite phase change material.

[0080] The latent heat of phase transition and phase transition temperature of the samples were determined using a TA Instruments DSC 250 differential scanning calorimeter (DSC) from the USA. The temperature range was -30 to 100 °C, and the heating / cooling rate was set to 5 °C / min. -1 Nitrogen atmosphere; results are shown in Table 2 and Figure 3 .

[0081] The thermal conductivity of the samples was tested using the transient planar heat source method with a HotDisk TPS2500S thermal constant analyzer (Sweden). A 5501 polyimide probe was used during the testing. All tested composite phase change material samples were cylindrical blocks with a diameter of 50 mm and a height of 10 mm. The results are shown in Table 2 and... Figure 4 .

[0082] The thermal performance parameters of pure phase change microcapsules (MPCM) and composite phase change materials prepared in Examples 1-10 are shown in Table 2.

[0083] Table 2 Comparison of thermal performance parameters of composite phase change materials

[0084]

[0085] Figure 3 The DSC curves of composite phase change materials with different MPCM contents are shown, where a represents SA / PCM and b represents FG / PCM. The results show that the DSC curves of both SA / PCM and FG / PCM exhibit sharp endothermic peaks and broad exothermic peaks similar to those of pure MPCM. With increasing MPCM content, the latent heat of both SA / PCM and FG / PCM shows a stable upward trend. Furthermore, in the FG / PCM composite phase change material, increasing the FG content reduces the undercooling (from 5.5℃ to 3.7℃).

[0086] From Table 2 and Figure 3 As can be seen, for pure MPCM, its melting / cooling temperatures are 29.1℃ / 23.2℃, and its melting / cooling enthalpies are 164.3 J·g. -1 / 166.3J·g -1 When the content of phase change components in SA / PCM and FG / PCM exceeds 70 wt%, the composite phase change material still maintains a high latent heat value (>100 J·g). -1 It exhibits excellent thermal storage capabilities.

[0087] Figure 4 The graph shows the thermal conductivity of composite phase change materials with different MPCM contents, where a represents SA / PCM and b represents FG / PCM. The scaffold structure formed by SA and FG significantly alters the thermal conductivity of the composite phase change materials, thus affecting the rates of heat absorption and release. Figure 4 As can be seen from Table 2, although n-octadecane / melamine resin MPCM has a high latent heat capacity, its low thermal conductivity (0.217 W·m) is a significant factor. -1 ·K -1 This limits its application in thermal management. SA has a temperature of 0.033 W·m. -1 ·K -1 The ultra-low thermal conductivity of composite phase change materials based on SA as the matrix can achieve a minimum of 0.0633 W·m. -1 ·K -1 The thermal conductivity of (SA / PCM-50) is similar to that of commonly available insulation materials. Conversely, due to the high thermal conductivity inherited from graphite, the thermal conductivity of FG / PCM composites is significantly improved. Compared to pure MPCM, the thermal conductivity of FG / PCM-70 and FG / PCM-50 increases to 1.752 W·m. -1 ·K -1 and 2.934 W·m -1 ·K -1 The increases were 807% and 1352%, respectively. This improvement is attributed to the continuous thermally conductive network formed by flake graphite and carbon fiber, which provides an effective heat transfer channel.

[0088] Thermogravimetric analysis (TGA) was performed using a Mettler Toledo TGA / DSC3+ thermal analyzer to evaluate the thermal stability of the composite material. The heating rate was 10 °C / min, and the test temperature range was from room temperature to 800 °C under a nitrogen atmosphere. Compressive strength was tested using a Model 5969 universal testing machine with a loading rate of 1 mm / min. The results are shown in [Figure number missing]. Figure 5 .

[0089] Figure 5 The graphs show the thermal stability and mechanical properties of SA / PCM and FG / PCM composite phase change materials, where a represents the thermal stability of TG and b represents the compressive stress-strain curve. Figure 5 Section a shows the thermogravimetric curves of microcapsule MPCM, SA / PCM (Example 3), and FG / PCM (Example 8) to evaluate the thermal stability of the composite materials. The SA / PCM and FG / PCM composite phase change materials exhibited similar thermal degradation trends to the pure MPCM microcapsules. However, it is noteworthy that during the MF degradation stage, the mass loss rate of SA / PCM was significantly lower than that of the other two materials. This may be attributed to the silica aerogel adhering to the microcapsule surface, acting as an "armor" to effectively protect the encapsulated MPCM and slow down the thermal decomposition rate. Above 500°C, the mass of each sample remained relatively stable, and the mass loss of SA / PCM and FG / PCM roughly corresponded to the proportion of MPCM added, indicating that their residual components were mainly silica aerogel and graphite. Since both materials exhibited excellent high-temperature stability under a nitrogen atmosphere, it can be confirmed that the prepared composite phase change materials possess good thermal stability and shape retention capabilities. Figure 5 As shown in section b, both SA / PCM and FG / PCM composites exhibit high compressive strength. SA / PCM, however, demonstrates significant brittleness, with a compressive strength of 8.56 MPa, but fractures after reaching its compressive limit, exhibiting a typical brittle failure mode. In contrast, FG / PCM-70 has a compressive strength of 7.87 MPa; the introduction of graphite endows the composite with excellent ductility, enabling it to withstand greater deformation before failure.

[0090] As can be seen from Examples 1-10, FG / PCM-50, FG / PCM-60, and FG / PCM-70 all exhibit high thermal conductivity and latent heat capacity. Meanwhile, SA / PCM-70 and SA / PCM-80 demonstrate outstanding performance among high-efficiency thermal insulation materials due to their low thermal conductivity and high latent heat characteristics. Considering the synergistic effect of thermal conductivity and latent heat capacity, Examples 8 (FG / PCM-70) and 3 (SA / PCM-70) were selected as representatives of high and low thermal conductivity PCMs, respectively. A pure silica aerogel barrier layer was added between the two layers of composite phase change material to construct a sandwich-structured composite material.

[0091] Example 11

[0092] A sandwich-structured composite phase change material for multifunctional thermal management comprises three layers: the first layer consists of nano-silica aerogel powder, chopped quartz fibers, and phase change microcapsules; the second layer consists of nano-silica aerogel powder; and the third layer consists of flake graphite, pitch-based carbon fiber chopped fibers, and phase change microcapsules. The mass percentages of nano-silica aerogel powder, chopped quartz fibers, and phase change microcapsules are 28.5%, 1.5%, and 70%, respectively; the mass percentages of flake graphite, pitch-based carbon fiber chopped fibers, and phase change microcapsules are 25%, 5%, and 70%, respectively; and the thickness ratio of the first, second, and third layers is 1:3:1.

[0093] A method for preparing sandwich-structured composite phase change materials for multifunctional thermal management, the process flow is as follows: Figure 1 The specific steps are as follows:

[0094] (1) Weigh each raw material accurately according to its mass percentage;

[0095] (2) In a beaker, nano-silica aerogel powder and short-cut quartz fiber are mixed to obtain an aerogel powder mixture; phase change microcapsules are added to the aerogel powder mixture and mechanically stirred for 30 minutes to ensure uniform dispersion to obtain a mixture; the obtained mixture is transferred to a mold of fixed size and pressed into shape using a compressor at 60°C with a pressure of 20MPa to a thickness of 6mm, and then cured at 60°C for 6 hours to form the first layer;

[0096] (3) Add new nano-silica aerogel powder to the first layer, and pressurize at 60°C for 2 hours to form the second layer with a thickness of 18mm.

[0097] (4) Add a mixture of flake graphite, pitch-based carbon fiber chopped fibers and phase change microcapsules to the second layer and pressurize it at 60°C for 6 hours to form a third layer with a thickness of 6 mm. After hot pressing, when the temperature drops to room temperature, continue to maintain the pressure for 4 hours to obtain a sandwich structure composite phase change material for multifunctional thermal management.

[0098] Comparative Example 1

[0099] A method for preparing a nano-silica aerogel heat insulation board: Weigh 202.5g of nano-silica aerogel powder and fill it into a square of a fixed size (150×150mm). 2 The nano-silica aerogel insulation board is formed by pressing it in a mold at 60°C under a pressure of 20 MPa to the required thickness (30 mm), and then curing it at 60°C for 6 hours to obtain a nano-silica aerogel insulation board with a density of 0.3 g·cm³. -3 .

[0100] Figure 6 This is a schematic diagram illustrating the effect of the sandwich-structured composite phase change material of this invention on building indoor temperature control and battery thermal management, where a represents building indoor temperature control and b represents battery thermal management. Figure 6 As can be seen from part a, when sandwich-structured composite phase change materials are used for building thermal management, the SA / PCM layer with low thermal conductivity can mitigate temperature fluctuations caused by solar radiation, thereby reducing the amount of heat entering the room. Meanwhile, the FG / PCM layer with high thermal conductivity can rapidly absorb indoor heat sources (including heat dissipation from people, lighting, and household appliances) and release excess heat at night to maintain a comfortable indoor temperature. Figure 6 As can be seen from part b, when sandwich-structured composite phase change materials are used for battery thermal management, FG / PCM can act as a heat dissipation channel during normal battery operation, quickly transferring and absorbing the heat generated by battery charging and discharging, and controlling the battery surface temperature. When thermal runaway occurs due to battery aging or other reasons, SA / PCM and nano-silica aerogel work together to provide thermal insulation and protection, preventing the chain reaction of battery accidents caused by the spread of thermal runaway. At the same time, nano-silica aerogel can also play a fire-retardant role, effectively preventing major accidents.

[0101] The surface temperature changes of nano-silica aerogel insulation panels and sandwich-structured composite phase change materials were compared under unidirectional transient thermal shock and multidirectional cyclic thermal environments to verify the temperature control capability of sandwich-structured composite phase change materials composed of composite phase change materials with different thermal conductivity under complex thermal environments.

[0102] Unidirectional transient thermal shock tests were conducted in a simulation apparatus, and samples of the same dimensions (150×150×30mm) were prepared. 3The nano-silica aerogel insulation board and sandwich structure samples were prepared, and a 3kW·m2 ... -2 The heat load, results are shown in Figure 7 Part a in the text.

[0103] Figure 7 Part a of the figure shows the surface temperature response curves of the nano-silica aerogel insulation board in Comparative Example 1 and the sandwich-structured composite phase change material in Example 11 under transient thermal shock. The results show that within 2000 s, the temperature of the heated surface of the sandwich-structured composite phase change material is consistently lower than that of the nano-silica aerogel insulation board. This is a result of the combined effect of the high thermal conductivity and latent heat capacity of FG / PCM, which allows for rapid absorption and dissipation of surface heat. In the sandwich-structured composite phase change material, the surface temperature of FG / PCM remains within the phase change temperature range for the first 500 s, then rises rapidly, but remains lower than that of the nano-silica aerogel insulation board. Furthermore, both materials exhibit good thermal control performance on the other side of the surface. However, because the heated surface temperature of the sandwich-structured composite phase change material is significantly lower, the temperature rise on its temperature-controlled surface is controlled within 3°C, indicating that this structure has excellent thermal insulation performance.

[0104] The temperature control performance of the sandwich structure material under a multidirectional heat source was studied using periodic square-wave thermal perturbation input. The heating duration was set to 5 minutes, followed by a 10-minute natural cooling period. The heat flux on the SA / PCM side of the sandwich structure composite phase change material was set to 100 W·m. -2 The heat flux on the FG / PCM side is set to 50 W·m. -2 The same thermal conditions were applied to both sides of the nano-silica aerogel insulation board, and the results are shown in the figure. Figure 7 Part b in the text.

[0105] Figure 7 Part b of the diagram shows the boundary heat flux and surface temperature distribution of the nano-silica aerogel insulation board in Comparative Example 1 and the sandwich-structured composite phase change material in Example 11 under multidirectional cyclic thermal perturbation. The results show that the surface temperature of the pure aerogel is consistently higher than that of the sandwich composite material throughout the experiment, with maximum surface temperatures of 28.3 °C and 23.4 °C, respectively. Under multidirectional thermal perturbation, the FG / PCM effectively transfers and absorbs surface heat, resulting in a smaller surface temperature rise. Simultaneously, the SA / PCM layer and the intermediate layer insulate the high heat flux from the FG / PCM, preventing potential latent heat depletion failure in the phase change material. The experimental results demonstrate that the composite phase change thermal management material with gradient thermal conductivity in this invention provides additional advantages in complex environments (e.g., thermal shock and multidirectional heat sources).

[0106] A heating film was used to simulate transient high-temperature heating conditions. A FLIR A615 infrared thermal imager was used to measure the surface temperature of the composite phase change material during heating, thereby investigating the thermal protection effect of the sandwich-structured composite phase change material on batteries under high-temperature thermal shock. In the experiment, nano-silica aerogel insulation panels of the same size and the sandwich-structured composite phase change material were placed between the heating surface and a copper plate for comparison. The copper plate simulated the battery pack requiring protection; its high emissivity ensured accurate temperature readings from the infrared camera. The results are shown in [Figure number missing]. Figure 8 .

[0107] Figure 8 Infrared images of the nano-silica aerogel insulation board in Comparative Example 1 and the sandwich-structured composite phase change material in Example 11 under transient thermal shock testing. Figure 8 It can be seen that the heated surface (bottom surface) rapidly reaches approximately 120°C after heating begins. Within the first 10 minutes, the temperatures of the temperature-controlled surfaces (top surfaces) of both materials are essentially the same. However, after 20 minutes of heating, the temperature of the sandwich-structured composite phase change material and the copper plate above it is significantly lower than that of the nano-silica aerogel insulation board. By 30 minutes, the surface temperature of the nano-silica aerogel insulation board is 35°C, while the surface temperature of the sandwich-structured composite phase change material is only 26°C. This phenomenon is mainly attributed to the phase change material encapsulated within the sandwich-structured composite phase change material. Compared to silica aerogel, which has lower thermal conductivity, the high latent heat of PCM significantly reduces the effective thermal diffusivity of the composite material, thereby enhancing its ability to withstand thermal shock in a short time. Furthermore, the insulation layer in the middle of the sandwich-structured composite phase change material acts as a secondary thermal barrier after the phase change, further delaying heat transfer within the material. Experimental results show that compared to traditional insulation materials, the sandwich-structured composite phase change material has significant advantages under transient thermal shock conditions, effectively reducing temperature fluctuations on both the heated and temperature-controlled surfaces. This characteristic makes it a promising candidate for applications such as battery thermal runaway protection.

[0108] The thermal management performance of sandwich-structured composite phase change materials applied to building insulation was evaluated through indoor testing. The experimental setup is shown below. Figure 9 In this device, the main body of the experimental platform consists of a sealed stainless steel cavity. Pipes are arranged on the inner wall of the cavity, and heating and cooling are achieved through circulating heat transfer oil to simulate a uniform and stable ambient temperature. The internal temperature of the cavity is precisely regulated by a control panel. The test sample is placed in the center of the cavity and surrounded by ceramic fiber insulation panels to form a closed space. The sandwich-structured composite phase change material serves as the wall of the simulated building. The outer surface of the ceramic fiber insulation panels exchanges heat with the environment through natural convection. The thermal conductivity of the ceramic fiber insulation panels is extremely low (<0.2 W·m). -1 ·K -1This design minimizes direct heat transfer between the interior and exterior of the cavity, allowing for a clear comparison of the effects of different thermal environments. A heating film is attached to the inner surface of the ceramic fiber insulation panel as an internal heat source. This film is powered by a programmable DC power supply, providing a constant heat flow output by adjusting the power. The heating film is kept 5 cm away from the test sample. The data acquisition system includes a data logger and six K-type thermocouples, positioned at key locations such as the center of the heating film and the inner and outer surfaces of the sample. The K-type thermocouples have a measurement accuracy of ±0.5℃. By monitoring the sample surface temperature, the temperature control performance of the sandwich-structured composite phase change material can be evaluated.

[0109] Using the summer day temperature of Xi'an on May 24, 2024 as the outside temperature, the average indoor heat source power density of residential buildings is set at 15 W·m³. -2 To simulate the internal heat source of the insulation wall, a nano-silica aerogel insulation board of equal thickness (30 mm) prepared in Comparative Example 1 was selected as a control group to compare and analyze the surface temperature changes of the inner wall. The results are shown in [Figure 1]. Figure 10 .

[0110] Figure 10 The temperatures of the nano-silica aerogel insulation board in Comparative Example 1, the sandwich-structured composite phase change material in Example 11, and the outdoor environment were compared in an indoor thermal management experiment of a building. The results showed that, starting at 8:00 AM, the temperature curve of the sandwich-structured composite phase change material exhibited a significant thermal buffer plateau, forming a temperature buffer lasting for over 10 hours, with the temperature consistently maintained within the phase change temperature range of SA / PCM and FG / PCM. This phenomenon is attributed to the heat storage process of the composite phase change material, confirming the temperature regulation capability of the sandwich structure. Furthermore, as the external temperature continued to rise, the synergistic effect of SA / PCM and the intermediate insulation layer effectively delayed the temperature rise inside the sandwich-structured composite phase change material. Experimental results showed that the surface temperature of the inner wall of the sandwich-structured composite phase change material remained lower than the external ambient temperature and the temperature of the pure insulation material (nano-silica aerogel insulation board) until 8:00 PM. This performance can be attributed to the synergistic effect of the heat storage effect on the outer side and the phase change heat absorption effect on the inner side. Compared to ambient temperature, the interior wall temperature of the sandwich-structured composite phase change material was reduced by approximately 10°C; compared to the nano-silica aerogel insulation board, its maximum temperature was reduced by 3.15°C, and the peak temperature was delayed by nearly 3 hours. After 11 PM, the interior wall temperature of the sandwich-structured composite phase change material exceeded that of the nano-silica aerogel insulation board. This is because the heat absorbed by the phase change material during the day is released at night, thus helping to maintain a comfortable indoor temperature at night, creating a passive thermal feedback regulation effect.

[0111] In summary, this invention uses a simple hot-pressing method to prepare sandwich-structured composite phase change materials with differentiated performance, which exhibit excellent thermal management capabilities and have broad application potential in various application scenarios.

[0112] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A sandwich-structured composite phase change material for multifunctional thermal management, characterized in that, The sandwich-structured composite phase change material consists of three layers: the first layer is composed of silica aerogel, quartz fiber and phase change microcapsules; the second layer is composed of silica aerogel; and the third layer is composed of flake graphite, carbon fiber and phase change microcapsules.

2. The sandwich-structured composite phase change material for multifunctional thermal management according to claim 1, characterized in that, The thickness ratio of the first layer, the second layer, and the third layer is 1:3:

1.

3. The sandwich-structured composite phase change material for multifunctional thermal management according to claim 1, characterized in that, The mass percentages of silica aerogel, quartz fiber, and phase change microcapsules in the first layer are 9.5–47.5%, 0.5–2.5%, and 50–90%, respectively.

4. The sandwich-structured composite phase change material for multifunctional thermal management according to claim 1, characterized in that, The mass percentages of the flake graphite, carbon fiber, and phase change microcapsules in the third layer are 5-45%, 5%, and 50-90%, respectively.

5. The sandwich-structured composite phase change material for multifunctional thermal management according to claim 1, characterized in that, The phase change microcapsules have an average particle size of 2–5 μm; the phase change microcapsules have a core-shell structure; the core material of the phase change microcapsules is n-octadecane, and the shell material is melamine resin.

6. The sandwich-structured composite phase change material for multifunctional thermal management according to claim 1, characterized in that, The quartz fiber has a diameter of 11 μm and a length of 3 mm.

7. The sandwich-structured composite phase change material for multifunctional thermal management according to claim 1, characterized in that, The carbon fiber is selected from pitch-based carbon fiber, which has a diameter of 11 μm and a length of 2 mm.

8. The sandwich-structured composite phase change material for multifunctional thermal management according to claim 1, characterized in that, The flake graphite has sheet diameters of 10 μm, 50 μm, and 100 μm, and a thickness of 2 μm.

9. The method for preparing the sandwich-structured composite phase change material for multifunctional thermal management according to any one of claims 1 to 8, characterized in that, Includes the following steps: (1) Weigh each raw material according to the proportion; (2) Mix silica aerogel and quartz fiber to form a matrix material; Phase change microcapsules are added to the matrix material and stirred to obtain a mixture; the resulting mixture is then pressed, molded, and cured to form the first layer. (3) Add silica aerogel to the first layer and hot press to form the second layer; (4) Add a mixture of flake graphite, carbon fiber and phase change microcapsules to the second layer and continue hot pressing; after hot pressing, wait for the temperature to drop to room temperature and continue to maintain the pressure for a period of time to obtain the sandwich structure composite phase change material for multifunctional thermal management.

10. The preparation method according to claim 9, characterized in that, In step (2), the pressing temperature is 60°C and the pressure is 20 MPa; and / or, the curing temperature is 60°C and the time is 6 hours; and / or, In step (3), the hot pressing temperature is 60℃, the pressure is 20MPa, and the time is 2h; and / or, In step (4), the hot pressing time is 6 hours; and / or the pressure is maintained for 4 hours.

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